COMBUSTION EQUIPMENT FOR JUDGING ABNORMALITY OR LIFE

Abstract

 Disclosed is a combustion appliance, which comprises:

a burner; a combustion fan for supplying air to, and exhausting air from the burner; an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and a controller for storing a reference air-flow rate for determining whether an abnormality or expiration of a lifetime has occurred when the combustion fan is rotated at a predetermined revolution rate, for determining there is no wind condition when a change in the air-flow rate, which is detected by the air-flow rate sensor when there are no revolutions or a specified number of revolutions by the combustion fan, is within a predetermined permissible range, and for determining an abnormality or an expiration of a lifetime has occurred when no wind condition is detected and when the air-flow rate, which is detected by the air-flow rate sensor for determining the predetermined revolution rate for the combustion fan, is lower than the reference air-flow rate. With this arrangement, it can be appropriately determined whether the relationship between the air-flow rate and the revolution rate for the combustion fan is preferable in a condition that is not affected by external wind condition, and an occurrence of an abnormality or the expiration of a lifetime can be precisely ascertained.

Description

FIELD OF THE INVENTION

[0001] The present invention relates to a combustion appliance, such as a water heater, a bath water heater or a space heating appliance, that controls an air-flow rate from the output of an air-flow rate sensor and a fuel supply quantity to perform combustion control for reducing exhausting volumes of toxic substances, such as carbon monoxide, hydrocarbon and nitrogen oxides.

BACKGROUND OF THE INVENTION

[0002] In Fig. 15 is shown the system configuration of a common water heater as an example combustion appliance. A burner 2 is located in the lower portion of a combustion chamber 1, and a combustion fan 3 is located beneath the burner to supply air and remove exhaust gasses. A revolution count sensor is provided for the combustion fan 3. A heat exchanger 4 for the supply of hot water is located in the upper portion of the combustion chamber 1. A water supply pipe 5 is connected to the input of the heat exchanger 4, and an input water temperature sensor 6, such as a thermistor, for detecting the temperature of the input water, and a water volume sensor 7 for detecting the flow rate of the input water, are provided along the water supply pipe 5.

[0003] A hot water supply pipe 8 is connected to the output of the heat exchanger 4. An output water temperature sensor 10, such as a thermistor, for detecting the temperature of the hot water output by the heat exchanger 4, and a water flow rate control valve 11 for controlling the rate of flow of the hot water output, are provided along the hot water supply pipe 8.

[0004] Solenoid valves 13 and a proportional control valve 14 for controlling the volume of the gas supplied are located along a gas supply way 12 of the burner 2. Pressure induction inlets for pressure induction pipes 20a and 20b of a differential pressure sensor 16, which serves as an air-flow rate sensor, are provided at the lower portion of the burner 2 and in a flueway 19. A difference between the pressures induced along the pressure induction pipes 20a and 20b in the lower portion of the burner 2 and in the flueway 19 is detected by the differential pressure sensor 16.

[0005] A sequential program for controlling the operation of a water heater is incorporated in a controller 15. The controller 15 also has a control circuit for controlling the operation according to the sequential program. The controller 15 receives information from the input water temperature sensor 6, the water flow rate sensor 7, the output hot water temperature sensor 10, the differential pressure sensor 16, and a remote controller (not shown), and controls the operations of the solenoid valves 13, the proportional control valve 14, the combustion fan 3, and the water flow rate control valve 11 to perform water heating and to supply hot water. Water passing through the heat exchanger 4 is heated by the burner 2 to a temperature set by a remote controller, etc. The hot water that is output by the heat exchanger 4 at the set temperature is supplied along the hot water supply pipe 8 to a desired location, such as a kitchen or a bathroom.

[0006] During this operation, the controller 15 controls the revolution of the combustion fan 3 in consonance with the combustion potential (combustion volume) of the burner 2. Provided for the controller 15 are combustion control data concerning a gas supply volume and a combustion potential shown in Fig. 12, and fan revolution control data concerning an air-flow rate (fan revolutions) and a combustion potential shown in Fig. 13. A required calorific value for increasing the input water temperature to the set temperature is continuously calculated by a calculation circuit in the controller 15. The degree of opening for the proportional control valve 14, i.e., the gas supply volume, is adjusted in consonance with the combustion potential for the required calorific value and the data shown in Fig. 12. The degree of opening for the valve is controlled by a valve opening current which is fed to the proportional control valve 14. At the same time, the revolution rate of the fan is controlled so as to maintain an air-flow rate that corresponds to the combustion potential and the data shown in Fig. 13, and the optimal air volume for burner combustion is supplied to the burner 2.

[0007] The air-flow rate is controlled based on a differential pressure detection signal output by the differential pressure sensor 16. More specifically, provided for the controller 15 are those data shown in Fig. 14 concerning the relationship between the differential pressure for the differential sensor 16 and the air-flow rate (the volume of air). The actual air-flow rate is acquired in accordance with the differential pressure value detected by the differential pressure sensor 16. Then, a difference between the required air-flow rate and the actually detected air-flow rate is calculated. The revolution rate of the combustion fan 3 is adjusted so as to correct for the difference and reduce it to zero, so that an air-flow rate that is appropriate for the combustion volume is supplied.

[0008] When the supply of air is appropriate for the combustion volume, the volumes of carbon monoxide, hydrocarbon and other nitrogen oxides in the exhaust, which are generated by the incomplete combustion of gas, are kept low.

[0009] Generally, when a water heater has been used for an extended period of time, the fin 9 in the heat exchanger 4 and the burner 3 become blocked with dust or soot. As this blockage gradually increases, the resistance to the flow of air likewise becomes greater, until finally, the supply of air is inadequate for efficient burner combustion, resulting in the abnormal operation of the appliance or the expiration of its useful lifetime.

[0010] Conventionally, whether or not an appliance is operating abnormally, or the end of its useful lifetime has been reached is determined in consonance with the total times of burner ignitions and the total combustion time. When this method is used, however, it is difficult to make an accurate evaluation of the useful lifetime of an appliance. Therefore, even when extensive blocking, or worse, of the heat exchanger 4, etc., adversely affects combustion, it can not be determined that the lifetime of the water heater has expired because the ignition times and the total combustion time have not been reached to the established reference values. As a result, a water heater in this case would be a dangerous condition, as the water heater would continue to be employed and, quite naturally, would produce a large volume of carbon oxides that would be expelled with the exhaust. On the other hand, even though the combustion process provided by a water heater may be satisfactory, the water heater may be discarded when it is determined, in consonance with reference values for ignition times and for total combustion time, that its useful lifetime has expired. In this case, it would not be an effective and economical use of the water heater.

[0011] The present invention focuses on the use of the differential pressure sensor 16 to control the air-flow rate of the combustion fan 3, and is related to a combustion appliance that can precisely detect the malfunctioning or the expiration of lifetime of a water heater by using a differential pressure detection signal from the differential pressure sensor 16. For convenience, the differential pressure sensor 16 is hereinafter referred to as an air-flow rate sensor 16.

[0012] Fig. 16 is a graph showing the relationship between the air-flow rate (the output measured by the air-flow rate sensor 16) and the revolution rate by the combustion fan. As is indicated by the solid line in the graph, the revolution rate of the combustion fan 3 required to obtain a specified air-flow rate is precisely acquired. As is described above, when the air flow resistance is increased, however, the revolution rate of the combustion fan 3 required to obtain a specified air-flow rate is also increased. That is, when the combustion fan 3 is rotated at a specified revolution rate, an air flow to be supplied is reduced.

[0013] The present inventors focused on that it can be determined that a malfunction, such as the expiration of the lifetime, of the combustion appliance has occurred when the relationship between the air-flow rate and the revolution rate of the combustion fan 3 becomes shifted to a certain degree from an appropriate relationship, then the air flow resistance is changed.

[0014] The present inventors also found that the movement of air outside the location where the combustion appliance is installed affects the output reading obtained by the air flow sensor 16 through the flueway 19.

[0015] The present inventors also found that the combustion appliance may not be necessarily discarded if only the relationship between the air-flow rate and the revolution rate of the combustion fan 3 is changed from the normal condition. In other words, even when the air-flow rate is reduced under the maximum revolution rate of the combustion fan 3, if the capability of the combustion is reduced, an air flow corresponding to the reduced combustion capability may be able to be supplied.

[0016] To resolve the conventional problems, it is one object of the present invention to provide a combustion appliance that can appropriately detect and monitor a condition with a high air-flow resistance in the appliance.

[0017] It is another object of the present invention to provide a combustion appliance that can detect an occurrence of an abnormality of the appliance by monitoring the external air movement, detecting the relationship between the output measured by an air-flow rate sensor and a fan revolution rate when there is no external wind condition, and determining whether the relationship is shifted from normal condition.

[0018] It is an additional object of the present invention for a combustion appliance that, when the relationship between an air-flow rate and a revolution rate of a combustion fan is shifted from the normal condition to the limit of a first range or over, an input-down operation can be performed to reduce the combustion capability, and that, when the relationship is shifted to the limit of a second range or over, the expiration of the lifetime can be determined and the halting of the combustion operation can be effected.

DISCLOSURE OF THE INVENTION

[0019] The basic principle of the present invention is that, when no movement of external air or no wind has been confirmed, the output value from the air-flow sensor and the output value of a fan revolution rate detector are monitored to detect an abnormality or the expiration of the lifetime. Therefore, a first method is used for monitoring an air-flow rate detected by an air flow sensor while a combustion fan is halted or rotated at a specified revolution rate, and a second method is used for monitoring the revolution rate detected by a fan revolution rate detector while a combustion fan is so rotated that the air-flow rate detected by an air-flow rate sensor is maintained at a specified value. The principle is the same for either method, and the arrangements of the present invention required for the use of both methods will, now be alternately explained.

[0020] According to one aspect of a first invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for determining there is no outside wind condition when a change in the air-flow rate, detected by the air-flow rate sensor during no revolution or a constant revolution rate of the combustion fan, is within a predetermined permissible range.

[0021] According to another aspect of the first invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate of the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for determining there is no outside wind condition when a change in the revolution rate, detected by the revolution rate detector during the combustion fan being so rotated that the air-flow rate detected by the air-flow rate sensor is maintained to a constant value, falls within a predetermined range.

[0022] According to the first invention, no movement of external air is easily detected.

[0023] According to one aspect of a second invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for storing a reference air-flow rate for determining whether an abnormality or expiration of a lifetime has occurred during the combustion fan being rotated at a predetermined revolution rate, for determining there is no wind condition when a change in the air-flow rate, detected by the air-flow rate sensor during no revolutions or a constant revolution rate of the combustion fan, is within a predetermined permissible range, and for determining an abnormality or an expiration of a lifetime has occurred when the air-flow rate, detected by the air-flow rate sensor during the predetermined revolution rate of the combustion fan and no wind condition being detected, is lower than the reference air-flow rate.

[0024] According to another aspect of the second invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate for the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for storing a reference revolution rate for determining whether an abnormality or expiration of a lifetime has occurred during the combustion fan being so rotated that a constant air-flow rate is detected by the air flow sensor, for determining there is no wind condition when a change in the revolution rate, detected by the revolution rate detector during the combustion fan being so rotated that a certain constant air-flow rate is detected by the air-flow rate sensor, is within a predetermined permissible range, and for determining an abnormality or expiration of a lifetime has occurred when the revolution rate, detected by the revolution rate detector during the combustion fan being so rotated that the constant air-flow rate is detected by the air-flow rate sensor, is higher than the reference revolution rate.

[0025] According to the second invention, the relationship between the air-flow rate and the revolution rate of the combustion fan during no wind condition can be appropriately monitored, and an abnormality or expiration of a lifetime can be appropriately detected.

[0026] According to one aspect of a third invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for storing a reference air-flow rate to determine whether an abnormality or expiration of a lifetime has occurred when the combustion fan is revolving at a predetermined revolution rate, and for determining an abnormality or expiration of a lifetime has occurred when a change in the air-flow rate, detected by the air-flow rate sensor during the predetermined revolution rate of the combustion fan, is within a predetermined permissible range, and when the air-flow rate detected by the air-flow rate sensor is lower than the reference air-flow rate.

[0027] According to another aspect of the third invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate for the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for storing a reference revolution rate to determine whether an abnormality or expiration of a lifetime has occurred when the combustion fan is so rotated that a constant air-flow rate is detected by the air-flow rate sensor, and for determining an abnormality or expiration of a lifetime has occurred when a change in the revolution rate, detected by the revolution rate detector during the combustion fan being revolving so that the constant air-flow rate is detected by the air-flow rate sensor, is within a predetermined permissible range, and when the revolution rate detected by the revolution detector is higher than the reference revolution rate.

[0028] According to the third invention, the detection that there is no movement of external air and detection that the relationship between an air-flow rate and a fan revolution rate is shifted from an appropriate value can be simultaneously performed.

[0029] According to one aspect of a fourth invention, the combustion appliance according to the second or the third invention further comprises a fuel controller for feeding sufficient fuel to the burner to supply a required caloric value. When the abnormality or the expiration of the lifetime is detected, the supply of the fuel to the burner is forcibly reduced by the fuel controller.

[0030] According to a modification of the combustion appliance of the fourth invention, provided are a first reference air-flow rate, and a second reference air-flow rate that is lower than the first reference air-flow rate. When the abnormality or the expiration of the lifetime is detected, and when the air-flow rate detected by the air flow sensor is lower than the first reference air-flow rate, the supply of the fuel to the burner is forcibly reduced by the fuel controller. When the air-flow rate detected by the air-flow rate is lower than the second reference air-flow rate, the supply of the fuel to the burner is halted by the fuel controller.

[0031] According to another aspect of the fourth invention, the combustion appliance according to the second or the third invention, further comprises a fuel controller for providing an adequate supply of fuel to the burner to maintain a required caloric value. When the abnormality or the expiration of the lifetime is detected, the supply of the fuel to the burner is forcibly reduced by the fuel controller.

[0032] According to another modification of the combustion appliance of the fourth invention, provided are a first reference revolution rate, and a second reference revolution rate that is higher than the first reference revolution rate. When the abnormality or the expiration of the lifetime is detected, and when the revolution rate detected by the revolution detector is higher than the first reference revolution rate, the supply of the fuel to the burner is forcibly reduced by the fuel controller. When the revolution rate detected by the revolution detector is higher than the second reference revolution rate, the supply of the fuel to the burner is halted by the fuel controller.

[0033] According to the fourth invention, even when the relationship between the air-flow rate and the fan revolution rate is shifted from an appropriate value, the operation can be continued and incomplete combustion can be avoided by forcibly reducing the supply of fuel.

[0034] According to a fifth invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for detecting an absence of wind condition when a change in the air-flow rate, detected by the air-flow rate sensor while the combustion fan is not revolving or is revolving at a constant revolution rate, is within a predetermined permissible range, for storing, as an initial value, the air-flow rate detected by the air-flow rate sensor while the combustion fan is revolving at a predetermined revolution rate at the time, and for detecting a deterioration in ventilation, after a predetermined time since the initial value being stored, when the absence of wind condition is detected and when the air-flow rate, detected by the air-flow rate sensor while the combustion fan is revolving at the predetermined revolution rate, is changed from the initial value by an amount that is equivalent to or greater than a reference value.

[0035] According to another aspect of the fifth invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate for the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for detecting an absence of wind condition when a change in a revolution rate, detected by the revolution rate detector while the combustion fan is so rotated that a constant reference air-flow rate is detected by the air-flow rate sensor, is within a predetermined permissible range, and storing, as an initial value, the revolution rate detected by the revolution detector at the time, and for detecting a deterioration in ventilation, after a predetermined time since the initial value being stored, when the absence of wind condition is detected and when the revolution rate by the revolution rate detector is changed from the initial value by an amount that is equivalent to or greater than a reference value.

[0036] According to the fifth invention, since an initial value for an air-flow rate is stored in a combustion appliance that has been installed, sensitivity of the air-flow rate sensor that differs depending on the combustion appliance and on the installation environment can be adjusted.

[0037] According to one aspect of a sixth invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate for the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for detecting an absence of wind condition when a change in the air-flow rate, detected by the air-flow rate sensor while the combustion fan is not revolving, is within a predetermined permissible range, and for storing, as a zero point, the air-flow rate detected by air-flow rate sensor when the absence of wind condition is detected.

[0038] According to the sixth invention, since a zero point correction or calibration associated with a secular change or age change of the air-flow rate sensor can be performed without being affected by an external movement of air, the occurrence of an abnormality or the expiration of a lifetime can be appropriately determined by employing the air-flow rate sensor.

[0039] According to one aspect of a seventh invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate for the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for storing a reference air-flow rate for determining whether an abnormality or an expiration of a lifetime occurs while the combustion fan is revolving at a predetermined revolution rate, and for determining the abnormality or the expiration of the lifetime has occurred when the air-flow rate, detected by the air-flow rate sensor while the combustion fan is revolving at the predetermined revolution rate, is continuously lower than the reference air-flow rate for a predetermined period of time.

[0040] According to another aspect of the seventh invention, a combustion appliance comprises:

a burner;

a combustion fan for supplying air to, and exhausting air from the burner;

a revolution rate detector for detecting a revolution rate for the combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for the burner; and

a controller for storing a reference revolution rate for determining whether an abnormality or an expiration of a lifetime occurs while the combustion fan is so revolving that a constant air-flow rate is detected by the air flow sensor, and for determining the abnormality or the expiration of the lifetime occurred when the revolution rate, detected by the revolution rate detector while the combustion fan is so revolving that the constant air-flow rate is detected by the air-flow rate sensor, is continuously higher than the reference revolution rate for a predetermined period of time.

[0041] According to the seventh invention, detection of a condition during which there is no wind condition, and detection of an abnormality or of the expiration of a lifetime can be easily performed at the same time through simply determining whether or not there is any movement of air.

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] 

Fig. 1 is a block diagram illustrating the essential portion of a combustion appliance according to a first embodiment of the present invention;

Fig. 2 is a block diagram illustrating a circuit for reducing a combustion capability of the combustion appliance according to the first embodiment;

Fig. 3 is an explanatory diagram showing a water heater in the first embodiment that has a lifetime determining function;

Fig. 4 is a graph for explaining the relationship between a wind velocity in the appliance installation environment and a fluctuation in the output of a differential pressure sensor for detecting an air-flow rate in the appliance;

Figs. 5A and 5B are graphs for explaining a characteristic for three-step combustion control of the water heater and a characteristic for combustion control when the capability of the water heater is reduced;

Fig. 6 is a flowchart for a first operation of the first embodiment;

Fig. 7 is a flowchart for the first operation of the first embodiment;

Fig. 8 is a flowchart for a second operation of the first embodiment;

Fig. 9 is a flowchart for a third operation of the first embodiment;

Fig. 10 is a flowchart for the third operation of the first embodiment;

Fig. 11 is a flowchart for a fourth operation of the first embodiment;

Fig. 12 is a graph showing the relationship between the combustion capability of the water heater and a supplied volume of gas;

Fig. 13 is a graph showing the relationship between an air-flow rate in the water heater and the combustion capability;

Fig. 14 is a graph showing the relationship between a differential pressure and an air-flow rate, which are detected by a differential pressure sensor for detecting an air-flow rate;

Fig. 15 is an explanatory diagram showing a water heater as a common combustion appliance;

Fig. 16 is a graph showing the relationship between a target output value of an air flow sensor and a fan revolution rate;

Fig. 17 is a block diagram illustrating the essential portion of a combustion appliance according to a second embodiment of the present invention;

Fig. 18 is a graph for explaining the relationship between input down data (first reference revolution rate) and lifetime determination data (second reference revolution rate), which are used while operating in a lifetime determination mode, according to the second embodiment;

Fig. 19 is a graph for explaining the relationship, according to the second embodiment, between a sensor output target value and an averaged fan revolution rate that is acquired for each sensor output target value;

Fig. 20 is a flowchart for an operation performed by the combustion appliance of the second embodiment;

Fig. 21 is a flowchart for an operation performed by the combustion appliance of the second embodiment;

Fig. 22 is a block diagram illustrating the essential portion of a combustion appliance according to a third embodiment of the present invention;

Fig. 23 is a flowchart for an operation according to the third embodiment;

Fig. 24 is a flowchart for an operation according to the third embodiment;

Fig. 25 is an explanatory graph showing data for acquiring a determination ratio, which serve as reference data for determining the magnitude of a change relative to an initial value for maintenance data that is fetched periodically at each interval;

Fig. 26 is a flowchart for an operation according to a fourth embodiment;

Fig. 27 is a graph for explaining the first operation of the first embodiment; and

Fig. 28 is a graph for explaining the first operation of the first embodiment.

BEST MODES FOR CARRYING OUT THE INVENTION

[0043] A first, a second, a third and a fourth embodiment of the present invention will now be described while referring to the accompanying drawings. As the same reference numerals used for the prior art are also used in the embodiments to denote corresponding or identical components, no explanation for those components will be given.

[0044] In the following embodiments, an air-flow rate detected by an air-flow rate sensor 16 is referred to simply as a detected air-flow rate or an air-flow rate sensor output. Depending on the type of air-flow rate sensor, its direct output can be either a voltage value or another physical quantity. Regardless of what physical quantity, it is apparent that the air-flow rate detection value output by the air-flow rate sensor, or simply the output of the air-flow rate sensor, means an air-flow rate that has been detected.

[0045] Similarly, the output of a combustion fan revolution rate detector, or a revolution rate detection value, means a revolution rate that has been detected

[First Embodiment]

[0046] Shown in Fig. 3, as an example combustion appliance according to the present invention, is a water heater that has means for determining the occurrence of an abnormality or the expiration of its lifetime. The water heater in this embodiment has a burner 2, the combustion capability of which can be switched. The combustion stages of the burner 2 are defined as stages A, B and C. The combustion for stage A is performed by opening only a capability switching valve 18a, which is a solenoid valve, etc. When capability switching valves 18a and 18b are opened, a two-stage combustion operation for stages A and B is performed. When capability switching valves 18a, 18b and 18c are opened, a full combustion operation for stages A, B and C is provided. The combustion capability of the burner 2 can be changed by switching these capability switching valves 18a, 18b and 18c. The combustion changes for the burner 2, i.e., the switching of the capability switching valves 18a, 18b and 18c, is controlled by a controller 15. Further, in this embodiment, a differential pressure sensor 16, serving as an air-flow rate sensor, detects a differential pressure between the upper and lower sides of the burner 2. In addition, the revolution rate for a combustion fan 3 is detected by a fan revolution rate sensor 28, such as a Hall IC.

[0047] The feature of this embodiment is that, the controller 15 has a means for determining whether or not an operating abnormality or the expiration of its lifetime of the water heater has occurred, in addition to the control of an air-flow rate for the combustion fan 3, which is based on a value detected by the differential pressure sensor 16, an air flow sensor.

[0048] The differential pressure sensor 16 used in this embodiment is substantially an air-flow rate sensor, and for convenience is hereinafter referred to as an air-flow rate sensor.

[0049] As is shown in Fig. 1, the characteristic means for determining whether or not an abnormality or the expiration of a unit lifetime has occurred includes a condition determiner 22, a memory 23, a combustion stop unit 24, a fan re-activator 25, an abnormality/lifetime determiner 26, and a timer 27. These components are functional parts of the controller 15.

[0050] In the memory 23 are stored a reference air-flow rate for determining for the water heater whether or not an abnormality or the expiration of its lifetime has occurred relative to a set fan revolution rate, which is provided in advance as a setting requirement. Also stored in the memory 23 are data, such as a permissible range for the fluctuation in the output of the air-flow rate sensor when there are zero revolutions of the fan and when there is a constant revolution rate that is provided in advance. Although the set revolution rate for the fan is determined as needed, in this embodiment it is set to the rated maximum revolution rate for the combustion fan 3, and an air-flow rate obtained at the rated maximum revolution rate is stored.

[0051] The condition determiner 22 identifies a stable, condition in which there is no wind and a windy condition for an appliance installation environment at a time when there are zero revolutions of the combustion fan 3, i.e., when the combustion fan 3 is not revolving. Fig. 4 is a graph showing the relationship, of the magnitude of a wind speed to the output of the air-flow rate sensor 16, that is obtained by an experiment when the water heater is exposed in the windy condition. As is apparent from the graph, in the windy condition the detected points for the air-flow rates detected by the air-flow rate sensor 16 are asymmetrically positioned in the upper and lower portions relative to the zero point of the sensor 16. The width of this fluctuation is increased as the wind speed is increased.

[0052] The condition determiner 22 compares the air-flow rate detected by the air-flow rate sensor 16 when there are zero revolution rate of the combustion fan 3, or the fluctuation width of the air-flow rate with a permissible range stored in the memory 23. The permissible range is set to determine whether there is a windy condition or a no-wind condition, depending on whether the fluctuation width of the air-flow rates is equal to or greater than a predetermined value, or that it is equal to or less than a predetermined value. The windy condition is determined, for example, by examining whether or not the fluctuation width of the detected air-flow rate exceeds a predetermined permissible value. The windy condition can also be easily determined by examining the detected air-flow rate to determine whether it exceeds a predetermined absolute value.

[0053] When a specified fan revolution rate, which is set in advance, is detected by the fan revolution rate sensor 28 in a condition where there is no combustion, the condition determiner 22 operates the timer 27 for a predetermined period of time. During the timer operation period, the condition determiner 22 compares the air-flow rate provided by the air-flow rate sensor 16 with the reference air-flow rate stored in the memory 23. When the detected air-flow rate is outside the permissible range, the condition determiner 22 detects that there is a windy condition. When the detected air-flow rate is within the permissible range, the condition determiner 22 detects that there is a stable, no-wind condition, and transmits the results to the combustion stop section 24 and the abnormality/lifetime determiner 26.

[0054] When, in the combustion operation where the combustion fan 3 is revolving at the rated maximum revolution rate, the combustion stop section 24 receives a result from the condition determiner 22 indicating that the detected air-flow rate is lower than the reference air-flow rate, the combustion stop section 24 halts the combustion at the burner 2 and transmits a combustion stop signal to the fan re-activator 25. Upon receipt of the combustion stop signal from the combustion stop section 24, the fan re-activator 25 activates the combustion fan 3 at the set revolution rate, i.e., the rated maximum revolution rate, without any combustion at the burner 2, and transmits a fan re-activation signal to the abnormality/lifetime determiner 26.

[0055] Upon the receipt of the re-activation signal, the abnormality/lifetime determiner 26 determines whether an abnormality or the expiration of the lifetime of a water heater has occurred when the condition determiner 22 has ascertained that there is a stable, no-wind condition, and when the detected air-flow rate is equal to or lower than the reference air-flow rate while the combustion fan 3 is being rotated at the rated maximum revolution rate. An abnormality/lifetime signal is thereafter output. On the other hand, when the condition determiner 22 determines there is a windy condition, or when the detected air-flow rate exceeds the reference air-flow rate, even though there is a stable, no-wind condition, the abnormality/lifetime determiner 26 ascertains that no abnormality has occurred in the water heater, or that the lifetime of the water heater has not yet expired, and an abnormality/lifetime signal is not output.

[0056] Fig. 2 is a circuit diagram illustrating an operation controller for a water heater when an abnormality/lifetime signal is output by the abnormality/lifetime determiner 26. This circuit includes a combustion capability down switching section 31, a capability characteristic graph selector 32, a fan controller 34, and a water flow rate controller 33.

[0057] When an abnormality/lifetime signal is output by the abnormality/lifetime determiner 26, the water heater for which an abnormality has occurred or for which the lifetime has expired can be discarded. However, the circuit shown in Fig. 2 enables such a water heater to be used temporarily until it is replaced by a new one, instead of immediately discarding it when an abnormality/lifetime signal has been output. In Fig. 2, when receiving an abnormality/lifetime signal, the combustion capability down switching section 31 reduces the combustion capability of the water heater by one level to avoid incomplete combustion at the burner 2 for an air-flow rate of the combustion fan 3. Upon receipt of an abnormality/lifetime signal, the combustion capability down switching section 31 reduces the combustion capability of, for example, a size 24 water heater (output 36,000 kcal/h) to that of, for example, a size 20 (output 30,000 Kcal/h). The reduced combustion capability is transmitted to the capability characteristic graph selector 32 and to the water flow rate controller 33. To reduce the combustion capability, only the fuel fed to the burner 2 need be reduced.

[0058] Control characteristic data for three-stage combustion capacities, as is shown in Fig. 5A, are provided for the capability characteristic graph selector 32. The characteristic line D₁ is a characteristic line at the first stage combustion for the combustion stage A of the burner 2; D₂, a characteristic line at the second-stage combustion for combustion stages A and B of the burner 2; and D₃, a characteristic line for the three-stage combustion for stages A, B and C. Overlapping portions ΔD and ΔD' are provided between the characteristic lines for the individual stages to smoothly perform conversion of the characteristic lines D₁, D₂ and D₃.

[0059] At the first stage combustion condition, for example, the start end position D_s of the characteristic line D₁ is the minimum capability point. The combustion capability is gradually increased until it reaches the maximum combustion capability for the first stage, which is the end position D_F of the characteristic line D₁. When a greater combustion capability is required, the capability of the burner 2 is switched to the two stage combustion of the stages A and B. The combustion characteristic line is changed from point D_f of the line D₁ to point D_P of the line D₂, and combustion is controlled according to the characteristic line D₂. When the capability of the burner 2 is changed from two stages to one stage, while the combustion is controlled according to the line D₂, the start end position D_s of the line D₂ is changed to point D_Q of the line D₁, and the combustion is controlled according to the characteristic line D₁. As is described above, although the combustion control line is changed as the capability is changed by stages, the overlapping portions ΔD and ΔD' are provided, so that the switching between the characteristic lines can be smoothly performed without causing hunting.

[0060] However, the combustion capability down switching section 31 changes the combustion capability in the lower direction, and the fuel supply volume (proportional control valve current) on the right of the line L in Fig. 5A is cut off. Then, the overlapping portions ΔD and ΔD', between the characteristic lines D₁, D₂ and D₃, disappear, and switching of the combustion characteristic lines can not be performed smoothly. To resolve this problem, when the down switching of the combustion capability is received from the combustion capability down switching section 31, and when a required combustion capability lies between the characteristic lines D₁, D₂ and D₃, the capability characteristic graph selector 32 selects the character line for a smaller combustion capability (selects D1 when required combustion capability P is located between the lines D₁ and D₂ in Fig. 5B), and combustion is controlled according to the selected characteristic line.

[0061] On the other hand, when a down switching signal for the combustion capability is received from the combustion capability down switching section 31, the water flow rate controller 33 compares a temperature set by a remote controller, etc., with an output hot water temperature detected by an output hot water temperature sensor 10. When the output water temperature detected by the output water temperature sensor is lower than the set temperature, the water flow rate controller 33 so restricts the water flow control valve 11 that, through the control valve 11, hot water is output at the set temperature. In other words, since the combustion capability is reduced, the amount of hot water is also reduced to maintain the set temperature.

[Operational Sequence for First Operation]

[0062] A first operation for this embodiment will now be described while referring to the flowchart in Figs. 6 and 7. The schematic flow for the first operation is as follows. When it is found during combustion that the air-flow rate detected by the air-flow rate sensor is reduced, combustion is temporarily halted and a diagnostic operation is performed. During the diagnostic operation, first, a fan is re-activated. When the air-flow rate detected for a specified revolution rate of the fan is within a predetermined range for a predetermined time period, it is assumed that there is no wind condition, and a check is performed to determine whether or not the current air-flow rate is lower than the reference air-flow rate. When the current air-flow rate is lower than the reference air-flow rate, the following combustion is continued in the combustion capability down mode. When it is further detected that the air-flow rate detected by the air-flow rate sensor is reduced, the same diagnostic operation is repeated. When as the result of the diagnosis, the current air-flow rate is lower than the reference air-flow rate, it is assumed that the lifetime of the appliance has expired and combustion is inhibited.

[0063] First, at step 101, a zero is set as an initial value for an abnormality/lifetime decision flag (LIFE). Since the processing at steps 102 through 120 is for normal combustion control, this processing will be explained only briefly. At step 102, water input is confirmed in accordance with a signal from the water flow rate sensor 7. At step 104, a feedforward (FF) caloric value, which is required for raising the input water temperature to the set temperature, is calculated; the ON/OFF states of the capability switching valves 18a through 18c are determined; the degree of opening of a proportional control valve is determined, and a proportional control valve current that corresponds to the degree of opening is supplied; a combustion fan is rotated at a pre-purge revolution rate; and the solenoid valve 13 is rendered on.

[0064] At step 105, a check is performed to determine whether or not a pre-purge period has elapsed. When the pre-purge period has elapsed, the revolution rate for the combustion fan is increased to a revolution rate for an ignition attempt, and the switching capability valve and an igniter are rendered on. At step 107, it is confirmed that ignition by a flame rod (not shown) was performed, and at step 112, the igniter is turned off.

[0065] If, at step 107, ignition is not confirmed, at step 108, a check is performed to determine whether or not the time period for the ignition attempt has elapsed. When the ignition period has not yet elapsed, the ignition attempt is repeated. When ignition is not confirmed even though it has been attempted, at step 109 the solenoid valve, the capability switching valves, and the proportional control valve are set to off. It is then ascertained that a hot water plug (not shown) at the distal end of a hot water pipe 8 is closed so that the water-flow rate sensor 7 does not detect a water flow. At step 111, the combustion fan is halted to await re-opening of the hot water plug.

[0066] When, at step 107, ignition has been confirmed, and at step 112 the igniter has been turned off, at step 113 a check is performed to determine whether or not a zero is set for the abnormality/lifetime determination flag. At this time, since at step 101 a zero has been set for the abnormality/lifetime flag, program control advances to step 114 whereat combustion operation is performed by both the feedforward (FF) control and the feedback (FB) control for a gas volume, and by the water flow rate control using the water flow rate control valve.

[0067] At step 115, during the combustion operation, a check is performed to determine whether or not the air-flow rate is appropriate for the burner combustion volume. Generally, the relationship

is established between the opening degree of the proportional control valve 14, i.e., the valve opening current I, and the air-flow rate. ΔP defines a differential pressure at an interval between the upper and the lower air passages, and corresponds to an air-flow rate. K is a proportional constant and is set in advance. When the relationship between the valve opening current I and the air-flow rate satisfies the above expression, the combustion volume is appropriate for the air-flow rate, and combustion is continued while fan control is maintained. In other words, this is an ideal combustion that is close to complete combustion, and less carbon monoxide, hydrocarbon, and nitrogen oxides are discharged in the exhaust. When the relationship does not satisfy the above expression, at step 117 the valve opening current I is compared with the air-flow rate information KΔP. When I is smaller than KΔP, it is assumed that the air-flow rate is too high relative to the degree of opening of the proportional control valve 14, i.e., the gas supply volume. In this case, at step 118, the revolution rate for the combustion fan 3 is reduced.

[0068] When the valve opening current I is greater than KΔP, at step 119 a check is performed to determine whether the fan revolution rate is equal to or greater than the rated maximum revolution rate. When the fan revolution rate has not reached the rated maximum revolution rate (upper limit value), the fan revolution rate can be increased. At step 120, therefore, the fan revolution rate is increased to compensate for an insufficient air-flow rate. When the fan revolution rate is equal to or greater than the upper limit value, it is assumed that the air-flow rate is insufficient (air volume is insufficient). Thus, program control moves to the confirmation processing to determine whether the insufficient air-flow rate is caused by the occurrence of an abnormality or the expiration of the unit's lifetime, or by the influence of wind in the environment in which the appliance is installed.

[0069] First, at step 121 in Fig. 7, a check is performed to determine whether a zero is set to the abnormality/lifetime flag. Since at step 101 a zero has been set to the flag, as described above, program control moves to the process at step 122, where the solenoid valve 13, the capability switching valves 18a through 18c and the proportional control valve 14 are rendered off to halt the combustion at the burner 2. At step 123, the combustion fan 3 is rotated in accordance with the set control condition, i.e., at the rated maximum revolutions in this example. At step 124, the air-flow rate ΔP detected by the air-flow rate sensor 16 is compared with the reference air-flow rate B mmAq. At step 125, until the operation time for the timer 27 has elapsed, sampling of the detected air-flow rate is repeatedly performed, and the result is compared with the reference air-flow rate.

[0070] When, during the timer operation period, all of the detected air-flow rates ΔP are lower than the reference air-flow rate, the condition determiner 22 determines that a condition exists in which there is no wind condition. Since an insufficient air-flow rate occurs even when there is no wind movement, it is detected that deterioration occurred due to ventilation blockage, such as the plugging of the water heater 4 with soot. At step 126, the abnormality/lifetime determiner 26 determines that an abnormality occurred in the appliance or that the lifetime of the appliance has expired, and a "1" is set to the abnormality/lifetime determination flag. On the other hand, if the detected air-flow rate ΔP is higher than the reference air-flow rate even once during the timer operation period (C minutes), it is assumed, at step 117, that the detected air-flow rate ΔP is higher than the reference air-flow rate I/K to the lower pressure side not because an abnormality has occurred in the appliance or because the lifetime of the appliance has expired, but because the detected air-flow rate is affected by a draft, such as when a reverse draft strikes the air exhaust side of the water heater, and is temporarily reduced. In the process at steps 123 through 125, determination of a stable, no wind condition and determination of the occurrence of an abnormality or the expiration of the lifetime of an appliance are performed at the same time. The reference air-flow rate is calculated based on, for example, the limiting value at which the carbon monoxide, hydrocarbon, and nitride oxide contents of the exhaust gas will be increased if incomplete combustion is continued and if an air-flow rate is lower than the current rate.

[0071] The process at step 124 will be further explained while referring to Fig. 27. Fig. 27 is a graph showing an example change in an air-flow rate when the fan was rotated at a specified revolution rate as time elapsed along the horizontal axis. When an air-flow rate higher than the reference air-flow rate B mmAq was detected, the appliance was in the normal state. The reference air-flow rate constantly fluctuated due to the influence of the external movement of air, as is shown in Fig. 27.

[0072] An example where the reference air-flow rate was affected by external wind condition was recorded during the C1 minute period. When external air is blown into the exhaust port, the detected air-flow rate goes low temporarily. However, as in the natural world, a constant, strong wind does not continuously blow in the same direction, the strength of an air current entering from the outside fluctuates, and the air-flow rate at times exceeds B mmAq, as is indicated for the period C1 in Fig. 27. As a result, a phenomenon occurs wherein the detected air-flow rate ΔP is higher than the reference value B mmAq. When this condition is detected it is determined that a windy condition exists.

[0073] After additional time had elapsed, an example recorded during the C2 minute period was acquired when there was no external movement of air and when the detected air-flow rate fell below the reference value B mmAq. In this case, since there was no external wind condition and since there was less fluctuation of the detected air-flow rate, at step 124, it is detected that the detected air-flow rate is lower than the reference air-flow rate, even though there is no wind condition.

[0074] As is described above, the determination of the wind condition and the determination that an abnormality or the expiration of a lifetime has occurred can be performed at the same time by monitoring whether or not an air-flow rate lower than the reference air-flow rate B is continuously maintained for a specified period of time.

[0075] In Fig. 28 is shown a change in the revolution rate for the combustion fan 3 that was recorded while the combustion fan 3 was so controlled that a constant air-flow rate was detected by the air-flow rate sensor. In this case, contrary to the preceding case, whether or not the revolution rate detected by the fan revolution rate detector is maintained and is greater than the reference revolution rate B for a constant period of time is determined, so that the determination of the wind condition and the determination whether an abnormality or the expiration of a lifetime has occurred can be performed at the same time.

[0076] Referring back to Fig. 7, when at step 126 it is detected that an appliance abnormality has occurred or that the lifetime has expired and an abnormality/lifetime signal is output, a signal to the effect that the appliance is operating abnormally or that its lifetime has expired is indicated by using a lamp, or is displayed on the screen of a remote controller, etc., to inform a user that an abnormality or the expiration of the lifetime of the appliance has occurred. In this manner, the user is notified that the performance of an appropriate procedure is required, such as the replacement or the maintenance of the appliance.

[0077] The occurrence of an abnormality or the expiration of the lifetime is determined at steps 122 through 126. When it is detected that an abnormality has not occurred or that lifetime has not yet expired, the abnormality/lifetime determination flag holds a zero. When it is detected that an abnormality has occurred or that the lifetime has expired, a "1" is set for the abnormality/lifetime determination flag.

[0078] In either case, a hot water plug is opened and the process at steps 102 through 113 is performed. When, at step 113, it is confirmed that a "1" is set for the abnormality/lifetime determination flag, it is assumed that the combustion operation was performed after the occurrence of an abnormality or the expiration of the lifetime of the appliance was detected. The process at step 127 and the following steps in Fig. 7 are performed.

[0079] The operation at step 127 and the following steps is to enable the water heater to be used temporarily within the reduced range of the air-flow rate due to the occurrence of an abnormality or the expiration of the lifetime of the appliance. At step 127, the combustion capability of the water heater is reduced by a predetermined value, e.g., to 1/N, for each stage of the burner 2. Here, N is a real number that includes a decimal fraction. In other words, as is shown in Fig. 5A, the capability on the right side of the line L is cut. Then, at step 128, a check is performed to determine whether or not the combustion capability obtained by feedforward calculation is available (feedforward gas control is enabled) relative to the set temperature. When the combustion capability is available, the combustion operation at step 115 and the following is performed for the condition where the combustion capability is cut. When, at step 116, it is determined that the water flow state is ON (combustion is continuing), program control does not go to step 113, but moves to step 115 in consonance with the combustion capability that is reduced to 1/N, as is indicated by the broken line.

[0080] At step 128, it may be determined that the combustion capability acquired by feedforward calculation is not available. More specifically, as is shown in Figs. 5A and 5B, the capability on the right side of the line L is cut, the overlapping portions ΔD and ΔD' disappear between the characteristic lines for the stages, and as a result, a combustion capability at a drop portion between a characteristic line for a low capability and that for a higher capability is required. In this case, at step 129, the characteristic line for combustion control is shifted to the characteristic line for low combustion. In order to compensate for a reduction in the temperature of supplied hot water, which is caused by selecting the characteristic line for the low capability, at step 130, the water flow control valve 11 is controlled to reduce the output of hot water, and the water flow rate is adjusted so that hot water at the set temperature can be output. The combustion operation at step 115 and the following is performed. Also in this case, if it is ascertained that the water flow state is ON at step 116, program control does not move to step 113 but goes to step 114.

[0081] After the abnormality/lifetime determination flag has been set to "1", as described above, the air-flow rate control is performed at steps 115 through 120. When at step 119 the fan revolution rate is equal to or greater than the rated maximum revolution rate, at step 121 a check is performed to determine whether or not the abnormality/lifetime determination flag is set to zero. Since in this stage the abnormality/lifetime determination flag has been set to "1" at step 131, the operation of the appliance is forcibly halted. The following combustion operation is thereafter inhibited, and as a result, incomplete combustion operation is avoided and safety is ensured.

[Operational Sequence for Second Operation]

[0082] Fig. 8 is a flowchart showing a second operation for determining whether an abnormality or the expiration of the lifetime of an appliance has occurred. The schematic processing flow for the second operation is as follows. When an abnormal air-flow rate is detected during the combustion, the combustion is temporarily halted. In a diagnostic process, the wind condition is examined with no combustion and no revolution of a combustion fan. When there is no wind condition, the combustion fan is rotated at a predetermined revolution rate, and a check is performed to determine whether or not a satisfactory air-flow rate is obtained.

[0083] In the first operation shown in Figs. 6 and 7, after the combustion was halted at step 122, the examination of the wind condition, and the determination of whether an abnormality or the expiration of the lifetime has occurred were performed at the same time, at steps 123 through 125. According to the second operation, however, the examination of the wind condition and the determination of whether an abnormality or the expiration of the lifetime had occurred are performed separately. As the wind condition can be more accurately determined, for this purpose, the second operation is more preferable. The other procedures are the same as those in the first operation, and the same step numbers as are used in the first operation are also used for those in the second operation. Since the procedures at steps 101 through 121 and at steps 127 through 131 are the same as those in the first operation, the procedures at steps 101, 102, 121 and 131 are shown in Fig. 8. The remaining procedures, which are performed in common with the first operation, are not shown.

[0084] In the flowchart in Fig. 8, at steps 132 through 139, the process is performed to determine what wind condition there is in the environment surrounding the installed appliance. At steps 140 through 142, the process is performed to determine whether an abnormality or the expiration of the lifetime has occurred. While combustion is taking place, at step 119 it is ascertained that, although the revolution rate for the combustion fan is equal to or greater than the rated maximum revolution rate, the detected air-flow rate is insufficient relative to the volume of the gas supplied. In this case, the combustion is halted at step 132 in order to determine whether the insufficiency of air is caused by some wind condition or by the occurrence of an abnormality or the expiration of the lifetime. When the combustion has been halted, the solenoid valve, the capability switching valves and the proportional control valve are rendered off, and the combustion fan 3 is also halted. Program control then moves to steps 133 through 139 to determine the wind condition status.

[0085] When external air is travelling at a specified wind velocity or higher, the output of the air-flow rate sensor 16 is affected by the wind condition and fluctuates widely, as was explained while referring to Fig. 4. In the following processing, the variable output of the air-flow rate sensor 16 is monitored, while the rotation of the combustion fan and the combustion are halted.

[0086] First, at step 133, maximum momentary value ΔP_MAX and minimum momentary value ΔP_MIN are input as initial data, and are stored in the memory 23. A value at the sensor zero point in Fig. 4, for example, is input as initial values for ΔP_MAX and ΔP_MIN. At step 134, a check is performed to determine whether the air-flow rate ΔP detected by the air-flow rate sensor 16 is equal to or greater than ΔP_MAX. If the detected air-flow rate ΔP is greater than the maximum momentary initial value ΔP_MAX, the detected value ΔP is replaced with the value ΔP_MAX. At step 136, the detected air-flow rate ΔP is compared with the minimum momentary initial value ΔP_MIN to determine whether the value ΔP is equal to or smaller than the value ΔP_MIN. If the value ΔP is smaller than the value ΔP_MIN, the ΔP is replaced with the value ΔP_MIN. The replacement of the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is performed during a predetermined sampling time period designated by the timer 27, and the values ΔP_MAX and ΔP_MIN are established.

[0087] Following this, a difference (the width of the fluctuation) between the established values ΔP_MAX and ΔP_MIN is calculated to determine whether or not the difference is below the set permissible range. When the difference between the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is equal to or exceeds the limit for the permissible range D, i.e., when the wind velocity causing the fluctuation in the air-flow rate detected by the air-flow rate sensor 16 is greater than the wind velocity corresponding to the permissible range D, it is detected that there is some wind condition, and it is assumed that the insufficient air volume is due to a temporary effect of the wind condition. The processing at step 102 and the following is thereafter performed.

[0088] If, at step 139, the difference between the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is less than D, it is ascertained that the condition is stable with no wind condition. At steps 140 and 141, processing is performed to determine whether an abnormality or the expiration of the lifetime of an appliance has occurred. At step 140, while the combustion at the burner 2 is being halted, the combustion fan 3 is rotated at the rated maximum revolutions that is the set control condition. At step 141, the detected air-flow rate ΔP is compared with the reference air-flow rate (B mmAq). When the detected air-flow rate ΔP is lower than the reference air-flow rate, it is assumed that an appliance abnormality has occurred or that the lifetime of the appliance has expired because of the deterioration of ventilation due to a blockage. A "1" is set for the abnormality/lifetime determination flag and an abnormality/lifetime signal is output. At step 127 and the following steps in Fig. 7, the combustion capability is reduced to 1/N, and a temporary combustion operation is permitted.

[Operational Sequence for Third Operation]

[0089] Figs. 9 and 10 are flowcharts showing a third operation according to the embodiment. The feature of the third operation is that, after the appliance has been powered on by an operation switch, the wind condition is examined prior to initiating the rotation of the combustion fan, and determination of an abnormality or the expiration of the lifetime of an appliance has occurred is performed during the pre-purge fan rotation. The same step numbers as are used for the first and the second operations are also used in the flowchart for the third operation to denote corresponding processes, and an explanation for these processes will not be given (or only a brief explanation will be given).

[0090] When the operation switch is turned on, at step 101, a zero is set for the abnormality/lifetime determination flag. At step 301, the initial values for the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN of the air-flow rate sensor 16 are input, and at the same time, a zero is set for a no-air-movement flag E. At step 302, the timer 27 for determining whether there is some wind condition or there is a stable is started (includes a reset start).

[0091] At steps 134 through 137, the processing is performed in the same manner as at steps 134 through 137 in Fig. 8 for the second operation. The air-flow rate detected by the air-flow rate sensor 16 is employed to establish the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN during the period of time allocated for sampling. At step 303, it is confirmed that the water flow rate sensor 7 is off. At step 304, a difference between the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is compared with the limit set for the permissible range D. When the fluctuation range between the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is below the limit set for the permissible range D, It is ascertained that the condition is stable and it is assumed that there is no wind condition, and a "1" is set for the no-air-movement flag E. If the fluctuation range between the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is equal to or exceeds the limit set for the permissible range D, it is assumed that there is some wind condition, and the zero for the no-air-movement flag E is maintained unchanged.

[0092] The determination of the wind condition is repeated until at step 307 an ON signal is transmitted by the water flow rate sensor 7. When the water flow rate sensor 7 is on, program control moves to step 104. Upon receipt of the ON signal from the water flow rate sensor 7, at step 104 pre-purge rotation of the combustion fan 3 is performed (the combustion fan is rotated to discharge exhaust gas from the combustion chamber before combustion of the burner is initiated). After the pre-purge fan revolution rate becomes stable, at step 308 in Fig. 10 the detected air-flow rate ΔP of the air-flow rate sensor 16 is compared with the reference air-flow rate (B mmAq) for the pre-purge constant speed. When the detected air-flow rate ΔP is less than the reference air-flow rate, at step 309, a check is performed to determine whether or not a "1" is set for the no-air-movement flag. When a "1" is set for the no-air-movement flag, it means that in the no-air-movement, stable condition the air flow rate has become insufficient. In such a case, therefore, it is ascertained that, because there is deterioration of ventilation due to a blockage, an appliance abnormality has occurred or the lifetime of the appliance has expired. At step 310, a "1" is set for the abnormality/lifetime determination flag, and an abnormality/lifetime signal is output. When, at step 308, the detected air-flow rate is equal to or larger than the reference air-flow rate, the air-flow rate is not insufficient. If, at step 309, a zero is set for the no-air-movement flag, it is ascertained that the air-flow rate insufficiency is caused by wind condition. In both of the above cases, it is assumed that neither indicate the occurrence of an abnormality or the expiration of the lifetime of the appliance, which is caused by the deterioration of the ventilation due to a blockage. The combustion operation at step 106 and the following steps is begun.

[0093] In the processing at step 106 and the following steps, when the abnormality/lifetime determination flag is set to zero, normal combustion is performed. When, at step 113, a "1" is set for the abnormality/lifetime determination flag, the processing indicated for steps 127 through 130 in Fig. 7 for the first operation is performed. In other words, the combustion capability of the appliance is reduced and the combustion operation is conducted.

[0094] According to the third operation, the wind condition is determined before the combustion fan 3 is rotated, and the occurrence of an abnormality or the expiration of the lifetime of the appliance is determined by using the pre-purge fan rotation before combustion at the burner 2 is begun. Compared with the first and the second operations, wherein combustion is temporarily halted and the combustion fan is rotated to determine whether an abnormality or the expiration of the lifetime has occurred, the determination of whether an abnormality or the expiration of the lifetime has occurred can be quickly performed in a short period of time. In addition, since, as well as in the second operation, the wind condition is determined while the combustion fan 3 is not revolving, the accuracy for the determination of the condition can be drastically increased.

[Operational Sequence for Fourth Operation]

[0095] Fig. 11 is a flowchart showing a fourth operation according to this embodiment. The feature of the fourth operation is that, when the air-flow rate insufficiency that can not be resolved by increasing the revolution rate of the combustion fan is detected during combustion, an occurrence of an abnormality or the expiration of the lifetime of the appliance is performed without halting the combustion operation. Then, a determination of wind condition or no wind condition and a determination of abnormality or lifetime expiration are performed during the combustion operation. The same step numbers as are used in the flowchart in Fig. 8 for the second operation are also used to denote the processes in the flowchart in Fig. 11, and no explanation for these process will be given or only a brief explanation will be given.

[0096] In the fourth operation, when an operation switch is turned on, at step 401, a zero is set for the abnormality/lifetime determination flag, and the initial values for the maximum momentary air-flow rate ΔP_MAX and the minimum momentary air-flow rate ΔP_MIN, both of which are detected by the air flow sensor 16, are input and stored. Then, the combustion operation is begun by performing the processing at step 102 and the following steps. The processing at steps 102 through 121 is the same as those at steps 102 through 121 in Fig. 8 for the second embodiment and in Figs. 6 and 7 for the first operation. When it is ascertained that the air-flow rate is insufficient relative to the supplied gas volume, at step 119, a check is performed to determine whether the revolution rate for the combustion fan 3 is equal to or greater than the rated maximum revolution rate. When the revolution rate of the combustion fan 3 is less than the rated maximum revolution rate, at step 120 the fan revolution rate is increased. If the fan revolution rate is equal to or greater than the rated maximum revolution rate, it is assumed that the air-flow rate can not be raised and is insufficient. Then, at step 121, a check is performed to determine whether or not a zero is held by the abnormality/lifetime determination flag. When a zero is held by the abnormality/lifetime determination flag, while the combustion operation is continued, the wind condition, and whether an abnormality or the expiration of the lifetime has occurred are determined. At steps 134 through 138, during the period of time allocated for sampling by a predetermined timer operation, the air-flow rate detected by the air-flow rate sensor 16 is employed to establish the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN.

[0097] Following this, at step 139, a difference between the maximum momentary value ΔP_MAX and the minimum momentary value ΔP_MIN is compared with the limit set for the permissible range D. More specifically, the fluctuation range for the air-flow rate, which is detected by the air flow sensor 16 when the combustion fan is revolving at a specified revolution rate, is compared with the limit set for the permissible range D. When the fluctuation range of the detected air-flow rate is below the permissible range, it is assumed that there is no wind condition. In the other cases, it is assumed that there is some wind condition.

[0098] When it is ascertained that there is a stable condition with no wind condition, at step 141 the air-flow rate ΔP detected by the air-flow rate sensor 16 is compared with the reference air-flow rate B mmaq. If the detected air-flow rate ΔP is smaller than the reference air-flow rate B mmAq, it means that the air-flow rate is insufficient, even though there is no wind condition, and it is assumed that an abnormality has occurred or that the lifetime has expired because of deterioration of the appliance due to blockage. At step 142, a "1" is set for the abnormality/lifetime determination flag, and an abnormality/lifetime signal is output. The processing for steps 127 through 130 in Fig. 7 is performed, and while combustion is continued, the combustion capability of the appliance is reduced.

[0099] When it is ascertained that the air-flow rate is insufficient in a condition where the air-flow rate can not be increased, unlike the first and the second operation where combustion is temporarily halted to determine whether an abnormality or the expiration of the lifetime has occurred, in the fourth operation the combustion operation is continued, while it is determined whether an abnormality or the expiration of the lifetime has occurred. Therefore, a situation does not occur where, during use, the supply of hot water is temporarily halted. The determination of whether an abnormality or the expiration of the lifetime of an appliance has occurred can be performed while the supply of hot water continues without interruption.

[0100] According to this embodiment, whether an abnormality or the expiration of the lifetime has occurred can be determined based on an air-flow rate detected by an air flow sensor for controlling the air-flow rate. Therefore, whether an abnormality or the expiration of the lifetime of an appliance has occurred can be precisely announced in consonance with the result of determination. As a result, it is possible to avoid a situation where when an appliance in which an abnormality has occurred or whose lifetime has expired, improperly continues to be used for combustion, which results in the excessive generation of CO gas. And also it is possible to avoid the unnecessary disposal of an appliance due to the determination that an abnormality has occurred in the appliance or that its lifetime has expired even though the appliance can still provide a satisfactory combustion function.

[0101] Further, the determination of whether an abnormality or the expiration of the lifetime of an appliance has occurred is performed under the stable conditions with no wind condition. The determination can therefore be performed without being affected by wind condition (fluctuation of the air flow sensor output due to the wind condition), such as a head wind, in the environment surrounding the installed appliance. Whether an abnormality or the expiration of the lifetime has occurred can be determined more accurately, and accordingly, the reliability of such a determination can be drastically increased.

[0102] For the determination of an occurrence of an abnormality or the expiration of the lifetime in this embodiment, according to the first operation, a C minute period is provided at step 125 in Fig. 7. When the detected air-flow rate ΔP exceeds the reference air-flow rate even once during this period, it is assumed that in an appliance there is no abnormality and that its lifetime has not expired. When all of the air-flow rates detected during the C minute period are less than the reference air-flow rate, it is assumed that an abnormality has occurred or that the lifetime has expired. However, as well as for the second through the fourth operations, without the provision of a C minute period, determination for an abnormality or expiration of lifetime may be performed based on the air-flow rate, which is detected after it has been determined there is no wind condition. On the other hand, in the second through the fourth operations, when the air-flow rate detected after it has been determined the condition is stable with no wind condition is lower than the reference air-flow rate, it is immediately assumed that an appliance abnormality has occurred or that the lifetime of the appliance has expired. As in the first operation, however, the specified C minute period may be provided, and if the detected air-flow rate exceeds the reference air-flow rate even once during this period, it is assumed that there is no appliance abnormality has occurred or that the lifetime of the appliance has not yet expired. When all the detected air-flow rates (detected differential pressure values) are below the reference air-flow rate (reference differential pressure value), it is assumed that an appliance abnormality has occurred or that the lifetime of the appliance has expired.

[0103] According to the first embodiment, a sensor for determining an occurrence of an abnormality or the expiration of the lifetime need not be provided separately. Since an air-flow rate sensor for controlling an air-flow rate can be employed for such determination, the structure of a combustion appliance, including a function for determining whether an abnormality or the expiration of the lifetime has occurred, is simplified, and accordingly, the manufacturing cost of the appliance can be reduced.

[0104] In addition, according to the first embodiment, the capability of a burner can be switched at multiple stages. When the abnormality/lifetime determiner outputs an abnormality/lifetime signal to reduce the combustion capability and a data absent portion occurs in the control characteristic data, and when the combustion capability at the data absent portion is required, capability adjustment means forcibly selects the control characteristic data on the lower side. As a result, even when the combustion capability at the data absent portion is required, combustion control characteristic data are always provided, and a smooth combustion operation can be performed without any problems.

[0105] In the first embodiment, the air-flow rate detected by the air-flow rate sensor at a constant fan revolution rate is monitored. Technically, however, it is obvious that the rotation of fan may be controlled so as to maintain a constant air-flow rate, and its revolution rate may be monitored.

[Second Embodiment]

[0106] A second embodiment of the present invention will now be described. The schematic description for the second embodiment is as follows. The features of the second embodiment are that the relationship between an air-flow rate and a fan revolution rate is monitored; that when there is an abnormality, an input down operation is performed; and that when the degree of the abnormality for the relationship is large, it is assumed that an abnormality has occurred in a combustion appliance or that its lifetime has expired and the operation is halted. More specifically, a first reference value and a second reference value are stored in advance. When a fan revolution rate for maintaining a predetermined air-flow rate exceeds the first reference value, fuel to be supplied to the burner is forcibly reduced. When the fan revolution rate exceeds the second reference value, supply of fuel is inhibited.

[0107] In the second embodiment, the determination of an occurrence of an abnormality or the expiration of a lifetime is performed by monitoring the revolution rate of a combustion fan while maintaining a constant output by an air flow sensor. In the first embodiment, such a determination is performed by ascertaining whether or not the output by an air flow sensor is reduced when a constant revolution rate of the combustion fan is maintained. It is obvious that technically the same result is obtained in both cases.

[0108] To simplify the explanation, "an occurrence of an abnormality or the expiration of a lifetime" is referred to simply as "the expiration of the lifetime."

[0109] In the second embodiment, during the combustion operation, a sensor output target value by an air-flow rate sensor is decided in consonance with a required combustion capability that is calculated for each value output. The rotation of the combustion fan is controlled so that the output of the air-flow rate matches the sensor output target value.

[0110] As is shown in Fig. 16, when, during combustion, the fan revolution rate exceeds a limiter provided for the upper side of fan control characteristic data, it is assumed that deterioration due to a ventilation blockage has occurred. The combustion operation is thereafter halted and the processing is performed in a lifetime diagnostic mode.

[0111] In the lifetime diagnostic mode, more than one type of combustion fan revolution rates are detected and stored for each of the sensor output target values V_S1 through V_SN, which are selected by a target value designation unit.

[0112] For detecting and storing the revolution rate for the combustion fan, a fluctuation range for fan revolution rate data is calculated according to a stored data effectiveness determiner, if it is has been incorporated. When the fluctuation range exceeds a fluctuation range set in advance, it is assumed that a wind is blowing in the environment in which the appliance is installed and causes fluctuation of the data. The data that are fetched are regarded as invalid data and are erased, and new data are fetched and stored. The revolution rate data for the combustion fan are detected in a stable condition, when there is no wind condition, and stored.

[0113] A lifetime determiner calculates the average of the revolution rates for the combustion fan monitored by the fan revolution monitor, and compares the average for the fan revolution rates with input down data and lifetime determination data for each sensor output target value. When, from among fan revolution rate averages for the individual sensor output target values, L₁ or more sets of data are entered in an area between input data and lifetime determination data, a down command for combustion capability is output. If, from among the fan revolution rate averages for the individual sensor output target values, the values of L₂ or more sets of data exceed those of the lifetime determination data, it is assumed that the lifetime of an appliance has expired and a lifetime signal is output. L₁ and L₂ are reference data set counts that are provided in advance.

[0114] In response to a combustion capability down command signal from the lifetime determiner, the combustion capability is reduced. Even if the air-flow rate is lowered, the combustion is performed while a preferable combustion function is maintained within the reduced air-flow rate range. When a lifetime signal is output by the lifetime determiner, it is assumed that the appliance has been locked by halting combustion. Combustion performed at an insufficient air-flow rate can be prevented so as to avoid the dangers associated with the increases in the amount of carbon monoxide, etc., that are generated.

[0115] The second embodiment will now be described in detail while referring to the drawings. The same water heater as is shown in Fig. 3 is employed as a combustion device for this embodiment. The same reference numbers as are used in Fig. 3 are also used to denote corresponding or identical components, and no explanation for them will be given.

[0116] Fig. 17 is a block diagram illustrating the structure of lifetime determination means, which is the characteristic component of the embodiment. The inherent lifetime determination means includes a combustion controller 1017, a fan rotation controller 1018, and a diagnostic mode operation unit 1021 for operating in an appliance lifetime diagnostic mode. The structures and the operations of the combustion controller 1017 and the fan rotation controller 1018 are the same as were previously described, and no explanation for them will be given.

[0117] The diagnostic mode operation unit 1021 includes a target value designator 1022, a fan rotation command unit 1023, a fan rotation monitor 1024, a lifetime determiner 1027, and a timer 1031. The processing by the diagnostic mode operation unit 1021 is performed when there is no combustion at a burner 2. The operation in the diagnostic mode is performed when the revolution rate of a combustion fan 3 during combustion has exceeded the upper limiter of the fan control characteristic data shown in Fig. 16 and combustion is thus halted. The limiter value is acquired from a boundary point at which the carbon monoxide, hydrocarbon, and nitrogen oxide contents of exhaust gas are increased due to incomplete combustion. The target value designator 1022 designates one or more sensor output target values of an air-flow rate sensor 16 to perform lifetime diagnosis. For the designation of such target values, sensor output target values to be designated may be input and stored in advance in memory, or the target values may be input externally by means of a keyboard or by using a memory card. The sensor output target values V_S1 through V_SN selected by the target value designator 1022 are transmitted to the fan rotation command unit 1023.

[0118] The fan rotation command unit 1023 collectively or sequentially transmits the sensor output target values V_S1 through V_SN to the fan rotation controller 18 within a predetermined period of time. Upon the receipt of the sensor output target value V_S1 from the fan rotation command unit 1023, for example, the fan rotation controller 1018 so controls the rotation of the combustion fan 3 that the output of the air-flow rate sensor 16 equals the sensor output target value V_S1. For the sensor output target value V_S2 received from the fan rotation command unit 1023, the fan rotation controller 1018 so controls the rotation of the combustion fan 3 that the output of the air-flow rate sensor 16 equals the value V_S2. In this manner, relative to the individual sensor output values V_S1 through V_SN from the fan rotation command unit 1023, at respective predetermined time intervals rotation of the combustion fan 3 for the different sensor output target values is performed.

[0119] The fan rotation monitor 1024 fetches one or more values for the revolution rate of the combustion fan 3 for each of the sensor output target values V_S1 through V_SN, and stores them in a memory. The timer 1031 is employed to store these fan revolution rates. The fan rotation monitor 1024 sequentially fetches the fan revolution rates R₁ through R_M at intervals of T seconds, and stores them in the memory. Each time the fan revolution rate for each sensor output target value is detected and stored by the fan rotation monitor 1024, the effectiveness determiner 1025 calculates, as a fluctuation range, a difference between the maximum revolution rate and the minimum revolution rate among the stored fan revolution rates R₁ through R_M, and determines whether or not the acquired fluctuation range is within a fluctuation range that is set in advance.

[0120] When the fluctuation range falls within the set fluctuation range, it is assumed that there is no wind condition in the environment wherein the water heater is installed, and the data detected and stored are reliable effective data. The result is transmitted to the fan rotation monitor 1024, which in turn detects and stores a fan revolution rate for the next sensor output target value. On the other hand, when the fluctuation range is shifted from the set fluctuation range, it is assumed that the condition is unstable due to wind condition.

[0121] When the fluctuation range for the fan revolution rate data, which have been detected by the fan rotation monitor 1024, is not within the set fluctuation range, the effectiveness determiner 1025 instructs the repeated erasure of the stored data, and again detects and stores fan revolution rates. When the fluctuation range of the fan revolution rate data falls within the set range, the detection and storage of the fan revolution rate for the next sensor output target value is instructed, and the fan revolution rate data for each sensor output target value are detected and stored under stable conditions while there is no wind condition.

[0122] As was previously described, from the graph in Fig. 4 it is apparent that under some wind condition conditions, the values detected by the air-flow rate sensor 16 vary vertically and asymmetrically relative to the zero point for the sensor, and the limits of their fluctuation are extended as the wind velocity increases.

[0123] The effectiveness determiner 1025 compares the fluctuation range of the values detected by the air-flow rate sensor 16 with a set fluctuation range (the set fluctuation range is defined by an upper limit level and a lower limit level, but may be defined by only an upper limit level). When the variance exceeds the set fluctuation range (when the variance exceeds the upper limit level if the set fluctuation range is provided only by the upper limit level), it is assumed that there is some wind condition. If the variance for the values (sensor output) detected by the air-flow rate sensor 16 falls within the set fluctuation range, it is assumed that the condition is stable and there is no wind condition. In other words, when the wind velocity in the environment wherein the heat water is installed is lower than a reference wind velocity corresponding to the set fluctuation range, it is assumed that there is no wind condition. When the wind velocity in the environment is higher than the reference wind velocity, it is assumed that there is some wind condition.

[0124] Data shown in Fig. 18 are provided in advance for the lifetime determiner 1027. More specifically, relative to the fan control characteristic data RI at the initial time when a water heater having no deterioration due to ventilation blockage is installed, input down data RB is provided on the side where the fan revolution rate is large at the same sensor output target value. Further, relative to the input down data, lifetime determination data RC is provided on the side where the fan revolution rate is large at the same sensor output target value. The input down data RB is a first reference value and the lifetime determination data RC is a second reference value. As is shown in Fig. 19, the lifetime determiner 1027 calculates the average values RA₁ through RA_N for fan revolution rate data that are detected and stored for each of the sensor output target values V_S1 through V_SN. The average values RA₁ through RA_N of the fan revolution rates for each sensor output target value are compared with the data shown in Fig. 18.

[0125] For the fan revolution rate average values RA₁ through RA_N of the sensor output target values V_S1 through V_SN, a check is performed to determine whether the number of average values dropped in an area between the input down data RB line and the lifetime determination data RC line is equal to or greater than preset number L₁ (L₁ is an integer of 1 or greater). When L₁ or more average values are present in the area, it is ascertained that the combustion is performed at an insufficient air-flow rate, and a down command signal for the combustion capability is transmitted to the combustion controller 1017.

[0126] A predetermined value is provided for the amount of a reduction in the combustion capability, and as a down command is issued for each reduction of the combustion capability, the combustion capability is reduced step by step. The amount of the combustion capability reduction is in proportion to the number of fan revolution rate average values that present in the area between the input down data RB and the lifetime determination data RC. Upon receipt of a combustion capability down command from the combustion capability down controller 1026, the combustion controller 1017 reduces a valve opening current, which is to be transmitted to a proportional control valve 14, with the equivalent amount of the combustion capability reduction, and reduces the volume of the gas supplied to the burner 2.

[0127] The lifetime determiner 1027 counts fan revolution average values RA₁ to RA_N, for each sensor output target value V_S1 to V_SN, that exceed lifetime determination data (lifetime determination data RC line). When the number of the average values is greater than a preselected number L₂ (L₂ is an integer of 1 or greater), it is assumed that, although the revolution rate for the combustion fan 3 has reached the upper limiter and can not be increased no further, the air-flow rate is insufficient because of deterioration due to the ventilation blockage, and the combustion function is degraded. As a result, a lifetime signal is output. Since the lifetime signal is output, a solenoid valve 13 is forcibly closed, supply of fuel is inhibited, and the water heater is locked by halting combustion. Thus, the combustion operation is hereinafter prevented.

[0128] When the fan revolution rate average values for each sensor output target value are not as large as those for the input down data RB, or when the number of the exceeded average values is less than L₁, even though their valves exceed those of the input down data RB, it is assumed that the water heater has not been degraded by ventilation blockage, and an appropriate (normal) signal is output.

[0129] A report unit 1030 receives signals concerning the results of determinations obtained by the lifetime determiner 1027, and communicates the determination results. The determination results obtained by the lifetime determiner 1027 are communicated by employing appropriate methods, such as the use of characters and symbols to display the results on a liquid crystal screen or the turning on a lamp or the blinking of a lamp, and the sounding of a buzzer to communicate the result of a lifetime determination.

[Description of Processing Using Flowcharts]

[0130] In the thus arranged second embodiment, processing for determining the expiration of a lifetime will now be described while referring to the flowcharts in Figs. 20 and 21. In Fig. 20, at step 1101, combustion for heating water is being performed. In this situation, the combustion controller 1017 supplies to the proportional control valve 14 a valve opening drive current in consonance with a required combustion caloric value. At step 1102, the sensor output target value for the air-flow rate sensor 16 in consonant with the required combustion caloric value is determined. At step 1103, a voltage to be applied to the combustion fan 3 is controlled so that the output of the air-flow rate sensor 16 equals the sensor output target value, and the rotation of the combustion fan 3 is controlled.

[0131] At step 1104, the fan revolution rate is detected. At step 1105, a check is performed to determine whether or not the detected revolution rate for the combustion fan 3 has reached the upper limiter for the fan control characteristic data shown in Fig. 16. When the fan revolution rate has not yet reached the upper limiter, it is assumed that the combustion operation is being performed at the normal air-flow rate, and the combustion operation is continued. If the fan revolution rate advances beyond the upper limiter, at step 1106 combustion is immediately halted, and program control is shifted to perform the lifetime diagnostic mode operations shown in Fig. 21.

[0132] For the lifetime diagnostic mode operations, first, at step 1201 in Fig. 21, the sensor output target values V_S1 through V_SN are set. Then, at step 1202, rotation of the combustion fan 3 is begun. The fan revolution rate is so controlled that the output of the air-flow rate sensor 16 equals the first sensor output target value V_S1. At step 1203, the timer 1031 which has been reset is turned on. When time T has elapsed, the fan revolution rate sensor 28 detects the revolution rate R₁ for the combustion fan 3, and stores it in the memory. The detection and storing of the revolution rate for the combustion fan 3 is repeated each T seconds, and M (an integer of 1 or greater) sets of detected fan revolution rate data, R₁ through R_M, are stored in the memory.

[0133] At step 1207, from among the stored fan revolution rate data R₁ through R_M, a difference between the maximum data value and the minimum data value is calculated to provide a fluctuation range value. A check is performed to determine whether or not the fluctuation range value is smaller than the fluctuation range value e that is set in advance. When the fluctuation range value is equal to or greater than e, it is ascertained that there is some wind condition, and M sets of fan revolution rate data R₁ through R_M, which are stored in the memory for the sensor output target value V_S1, are erased. At step 1201, the sensor output target value V_S1 is again designated, and the processing for detecting and storing the fan revolution rates at steps 1202 and the following steps is performed. At step 1207, again, a check is performed to determine whether or not the fluctuation range value for the data detected and stored is smaller than the set fluctuation range value e. If the fluctuation range value is outside the fluctuation range e, the detection and storing of the fan revolution rates at the sensor output target value is repeated.

[0134] When, at step 1207, it is ascertained that the fluctuation range value is within the fluctuation range e, it is assumed that there is no wind condition, and the fan revolution rate data detected at the sensor output target value V_S1 are regarded as effective data. At step 1208, the average value RA₁ is calculated for the data R₁ through R_M that have been detected and stored.

[0135] At step 1209, a check is performed to determine whether or not the number N for the fan revolution rate average values equals N, which is the number of the sensor output target values V_S1 through V_SN. In this embodiment, N = 1 when the average RA₁ of the fan revolution rates at the sensor output target value V_S1 is acquired. At step 1210, assuming that N is obtained by incrementing N by one, N = 2. At step 1201, the sensor output target value V_S2 is selected, and the rotation of the combustion fan 3 is so controlled that the output value of the air-flow rate sensor 16 is V_S2. Using the same process as that used for sensor output target value V_S1, the fan revolution rates R₁ through R_M are detected at the sensor output target value V_S2 and stored. Further, the fan revolution rate data are acquired and stored while there is no wind condition and while the fluctuation range value does not exceed the fluctuation range value e. At step 1208, the average value RA₂ for the data R₁ through R_M is acquired.

[0136] After the acquisition of the average revolution rate values RA₁ through RA_N, which correspond to the sensor output target values V_S1 through V_SN, at step 1211 the determination of the expiration of the lifetime is performed. In the processing for determining expiration of lifetime, the average fan revolution rates RA₁ through RA_N, which are acquired for the corresponding sensor output target values V_S1 through V_SN, as is shown in Fig. 19, are compared with the input down data RB and the lifetime determination data RC in Fig. 18. For example, RA₁ is compared with the input down data RB₁ and lifetime determination data RC₁. Similarly, the average value RA₂ for the fan revolution rates at the sensor output target value V_S2 is compared with the input down data RB₂ and the lifetime determination data RC₂.

[0137] As is described above, the average values RA₁ through RA_N, for the respective sensor output target values V_S1 through V_SN, are compared with the input down data RB₁ through RB_N and lifetime determination data RC₁ through RC_N for the corresponding sensor output target values. Among the average values RA₁ through RA_N, the average fan revolution rates located in an area between the input down data RB line and the lifetime determination data RC line are counted. If the count of the average values located in that area is equal to or greater than reference number L₁, which is provided in advance, a combustion capability down command signal is output. When L₂ (a reference number provided in advance) or more average fan revolution rates are present in an area above the lifetime determination data RC line, it is assumed that the lifetime of the appliance has expired, and a lifetime signal is output.

[0138] In response to a combustion capability down command signal, as was previously described, the combustion capability is reduced, the volume of the gas being supplied is reduced to avoid the inadequate supply of air, and the next combustion operation is enabled. When the lifetime signal is output, the appliance is locked in the combustion stop state, i.e., combustion is not enabled, so that combustion is prevented while deterioration of the appliance occurs due to the obstruction of ventilation. The results obtained through the lifetime determination operation are identified and reported by the report unit 1030.

[0139] According to the second embodiment, when the ventilation blockage is more or less advanced even though the lifetime of the appliance has not expired, and when combustion is being performed with an inadequate air-flow rate, a combustion capability down command signal is output to reduce the combustion capability. Therefore, the combustion operation can be continued while the air supply inadequacy is resolved. Since the degradation of the combustion is resolved, so that the water heater can be used until it is replaced by a new one, this is very convenient.

[0140] Further, since in this embodiment the operation in the diagnostic mode for the lifetime of the appliance is performed while combustion at the burner is halted, the lifetime diagnosis operation is performed more reliably. As is well known, the air flow resistance along an air path (air passage) that runs from the combustion fan 3 to an exhaust path 29 is different when there is combustion at the burner 2 and when combustion is halted. The air flow resistance when there is combustion at the burner is increased and is greater than that when combustion is halted. The increase in the air flow resistance varies depending on the caloric combustion value. In this embodiment, since the lifetime determination is performed while combustion is halted, i.e., under the constant conditions where there is no fluctuation of the exhaust air resistance in the path, the lifetime determination can be performed more accurately and reliably.

[0141] Although a plurality of sensor output target values have been designated in the above embodiment, only one sensor output target value may be selected. Further, although a plurality of fan revolution rates R₁ through R_M are detected for each sensor output target value in this embodiment, detection of only one fan revolution rate may be performed. In such a case, calculations to produce average values are eliminated, and in this invention the detected data is the equivalent of an average value. In other words, the detection of the fan revolution rate is equivalent to the operation for calculating the average value of the fan revolution rates. When a single sensor output target value is designated and only one fan revolution rate is detected to determine the expiration of a lifetime, the determination processing can be performed in a short time. However, if a plurality of the sensor output target values are designated and a plurality of fan revolution rates are detected, as in this embodiment, the determination of the lifetime can be performed more accurately.

[0142] In addition, in the second embodiment, when the fan revolution rate for the combustion fan 3 exceeds the upper limiter for the fan control characteristic data, the combustion is immediately halted and the operation is shifted to the lifetime diagnosis processing. For another example case, when the fan revolution rate exceeds the upper limiter, a lifetime diagnosis instruction flag may be set, and the lifetime diagnosis may be performed at an appropriate occasion, such as when the appliance is not being used after combustion has been halted, or before combustion is next initiated. To perform lifetime diagnosis after the appliance has been activated, combustion is not halted, even though the fan revolution rate exceeds the upper limiter, and the appliance can be continuously used. A user does not experience any inconvenience when using the appliance, and its usability is improved. In this case, the following processing may be performed. The degree of safety is determined in consonance with how much the fan revolution rate exceeds the upper limiter. In the most critical condition, combustion is immediately halted to perform lifetime diagnosis. In a less (lower) critical condition, combustion is continued and the lifetime diagnosis is performed at an appropriate time after the use of the appliance is ended.

[0143] Furthermore, in the above embodiment, the upper limiter for the fan control characteristic data provided to prevent the runaway of the combustion fan 3 has been employed as an upper limiter for a fan revolution rate that serves as a reference for lifetime diagnosis. A special upper limiter for lifetime diagnosis is set separately from the upper limiter for runaway prevention, and when the fan revolution rate exceeds the special upper limiter for lifetime diagnosis, the lifetime diagnosis may be performed in the above described manner.

[0144] In the above embodiment, the combustion fan has been so rotated as to maintain the target value for an air-flow rate, and the revolution rate has been monitored. Technically, a method whereby an air-flow rate detected by the air-flow rate sensor is monitored while a constant revolution rate for the combustion fan is maintained can provide the same result. In this case, the input down data is the first reference air-flow rate that is lower than an appropriate air-flow rate, and the lifetime determination data is a second reference air-flow rate that is lower than the first reference air-flow rate. When the air-flow rate detected by the air-flow rate sensor when the combustion fan is rotated at a specified revolution rate is lower than the first reference air-flow rate, the operation is performed in the input down mode. When the detected air-flow rate is lower than the second reference air-flow rate, the supply of fuel to the burner 2 is inhibited.

[Third Embodiment]

[0145] A third embodiment of the present invention will now be described.

[0146] According to the outline of the third embodiment, during the initiation period for a combustion appliance, an air-flow rate when a combustion fan is rotated at a constant revolution rate during is no wind condition is stored as an initial value. Periodically, for each time interval, the air-flow rate is measured under the same conditions. The obtained air-flow is compared with the stored air initial flow rate to perform lifetime determination.

[0147] In the third embodiment, a plurality of outputs by an air-flow rate sensor 16 are obtained at a time that a combustion fan is not being rotated, such as at the time of shipping of a combustion appliance or at a time when there is no combustion at a burner after its installation. When the fluctuation in the detected outputs is within a permissible range, a condition determiner ascertains that there is no wind condition.

[0148] Based on the detected output of the air-flow rate sensor under the stable conditions with no wind condition, the initial sensor value for such conditions is established and stored in the memory.

[0149] A combustion fan is rotated under set reference conditions and without combustion being initiated at a burner. When the condition determiner ascertains the conditions are stable and there is no wind condition, the output of the air-flow rate sensor is fetched. Based on the detected data, an initial value is established that serves as a reference for determining whether there is degradation of ventilation, and is stored in the memory.

[0150] After the initial sensor value obtained while there is no wind condition and the initial value for determination of ventilation deterioration have been established, periodically at each interval that is set in advance, the output of the air-flow rate sensor, detected at the time there is no combustion at a burner and no rotation of a combustion fan, is employed to determine the wind condition. When it is ascertained that the conditions are stable, with no wind condition, a fluctuation of the sensor output value relative to the initial value is calculated. If the fluctuation value exceeds a reference value provided in advance to determine the condition of the sensor, it is assumed that the sensor is faulty, and a determination signal is output.

[0151] In case the sensor is not faulty, the combustion fan is rotated, with no combustion at the burner, under the same reference conditions as when the initial value was established. The output of an air supply volume sensor under the stable conditions, with no wind condition, is fetched as maintenance data. The fluctuation of the maintenance data relative to the initial value, or the value for fluctuation between the maintenance data fetched at the current interval and the maintenance data fetched at the preceding interval, is obtained. When the fluctuation value exceeds the reference value provided in advance, a signal is output warning that the deterioration of ventilation due to a blockage has occurred.

[0152] After the warning signal has been output, when the normal combustion operation is being performed by combustion at the burner, the driving requirement for the combustion fan is detected. If the detected driving requirement exceeds the upper limit of a control range, a signal warning of the expiration of the lifetime of the appliance is output, a danger notice is displayed on an appropriate display means, and the combustion operation is forcibly halted.

[0153] The third embodiment will now be described while referring to the drawings. In Fig. 22 is shown the characteristic structure of this embodiment wherein provided are a sampling unit 2025, a condition determiner 2026, an initial value establishing unit 2027, a memory 2028, a fan driver 1019, a sensor fault determiner 2030, a lifetime determiner 2031, a ventilation deterioration determiner 2032, an input down controller 2033, display means 2034, and a timing mechanism 2035. These components function in consonance with a sequence program stored in the memory of a controller 15.

[0154] The sampling unit 2025 fetches the output of an air-flow rate sensor 16 by using the timing mechanism 2035, such as a timer, each time the appliance is powered and each time a predetermined time interval, such as one day, one week, or one month, provided in advance, has elapsed since the power-ON time. The output is transmitted as needed to the condition determiner 2026, the initial value establishing unit 2027, the input down controller 2033 and the ventilation deterioration determiner 1032.

[0155] As is shown in Fig. 4, the permissible range e for the fluctuation in the outputs of the air-flow rate sensor 16 during is no wind condition is provided in advance for the condition determiner 2026. As is well known, an environmental situation where a water heater is installed outdoors, wind flows into the appliance and causes the output of the air-flow rate sensor 16 to fluctuate even though the combustion fan 3 is halted. In this embodiment, a time when there is no change in the output of the air-flow rate sensor 16, i.e., when there is no wind condition, is detected and the output of the air-flow rate sensor 16 is employed as effective data.

[0156] More specifically, the condition determiner 2026 fetches a plurality of the outputs by the air-flow rate sensor 16 at predetermined time intervals (for example, 10 sets of data at 0.1 second interval). If the variation in the readings for the plurality of data sets, i.e., a difference between the maximum value and the minimum value of data that are fetched, is within the permissible range e, the condition determiner 2026 ascertains that the condition is stable with no wind condition. If a difference between the maximum value and the minimum value of data that are fetched exceeds the permissible range e, the condition determiner 2026 ascertains a condition with some wind condition. The results of the determination are transmitted to the initial value establishing unit 2027 and the ventilation deterioration determiner 2032. In this case, only a result obtained when there is no wind condition may be transmitted to the initial value establishing unit 2027 and the ventilation deterioration determiner 2032.

[0157] In the initial period following the installation of the appliance, i.e., in a period during which there is no deterioration of the ventilation due to blockage, and when the condition determiner 2026 has ascertained the condition is stable with no wind condition, in consonance with the output of the air-flow rate sensor 16 obtained during no combustion at the burner 2 and no rotation of the combustion fan 3, the initial value establishing unit 2027 designates the output of the air-flow rate sensor 16 at that time as a initial sensor value, and stores it in the non-volatile memory 2028. In this embodiment, the minimum value or the average value of a plurality of sets of fetched data is regarded as an initial value. When the condition determiner 2026 detects a condition with some wind condition, the data are not adopted.

[0158] After the initial sensor value output during no wind condition has been designated as the initial value by the initial value establishing unit 2027, the combustion fan 3 is rotated under the standard set condition with no combustion at the burner 2, i.e., at the maximum fan revolution rage in the control range for this embodiment. A plurality of outputs by the air-flow rate sensor 16 are fetched through the sampling unit 2025 at a specified sampling timing set in advance. It is confirmed that, based on the fetched data, the condition determiner 2026 has ascertained the condition is stable with no wind condition. Based on these outputs by the air-flow rate sensor 16 that are fetched (fetching of the detected data is not performed when there is any wind condition), the initial value for sensor output at the maximum revolution rate for the combustion fan 3 is established as a reference value for determining the deterioration of ventilation, and is stored in the memory 2028.

[0159] When the initial value has been established by the initial value establishing unit 2027, the fan driver 2029 receives, from the establishing unit 2027, an instruction to rotate the combustion fan 3 at the maximum revolution rate, and rotates the combustion fan 3 in accordance with the instruction. Besides an instruction from the initial value establishing unit 2027, the fan driver 2029 receives a fan drive instruction from the ventilation deterioration determiner 2032, and rotates the combustion fan 3 at the maximum revolution rate within a control range.

[0160] After the initial sensor value and the initial value for determining deterioration of ventilation have been established, the ventilation deterioration determiner 2032 fetches the output of the air-flow rate sensor 16 at predetermined time intervals. When it is ascertained by the condition determiner 2026 that a stable condition with no wind condition exists, an instruction is transmitted to the fan drive 1019 to rotate the combustion fan 3 at the maximum revolution rate, as the basis for the setting standards requirement.

[0161] While the combustion fan 3 is being rotated at the maximum revolution rate, and combustion at the burner 2 is not being performed, and when the condition determiner 2026 has ascertained that a stable condition with no wind condition exists, the ventilation deterioration determiner 2032 fetches the output of the air-flow rate sensor 16 through the sampling unit 2025 at predetermined sampling times. The fluctuation of the output of the air-flow rate sensor 16, relative to the initial value for determining the deterioration of ventilation, is calculated. In this embodiment, an absolute value for a difference between the initial value and maintenance data value is calculated as the fluctuation value. This fluctuation value is compared with the reference value provided in advance. When the fluctuation value is greater than the reference value, it is assumed that a blockage has occurred and is causing deterioration of the ventilation in the appliance, and a signal warning of deterioration due to the blockage is output. The deterioration of the ventilation in the appliance may be caused by soot that blocks the heater water 4, or by the deposit of dust in an air inlet (not shown), on a curved portion of blades of the combustion fan 3, or in a hole punched in metal (not shown). The deterioration of ventilation may also be caused by the attachment of dust to the burner 2.

[0162] Upon receipt of the signal from the ventilation deterioration determiner 2032 warning that there is deterioration of ventilation, the lifetime determiner 2031 detects the revolution rate for the combustion fan 3 while combustion is taking place at the burner 2, and determines whether or not it exceeds the maximum revolution rate, which is the upper limit for the control range. When the revolution rate exceeds the upper limit for the control range, it is assumed that ventilation in the appliance is blocked and an air volume required for combustion can not be supplied. A danger warning signal is output, and combustion at the burner of the water heater is immediately halted. A function that hereinafter does not accept a combustion instruction is performed to disable the following combustion operation of the appliance.

[0163] The input down controller 2033 calculates a ratio for maintenance data value fetched at periodic intervals to the initial value. When the obtained ratio is smaller than a reference ratio provided in advance, it is assumed that ventilation is considerably deteriorated due to blockage with soot, even though the lifetime has not yet expired. Even when blockage of the ventilation has occurred, in order to obtain the air volume required for combustion, the valve opening current to the proportional control valve 14 is controlled to restrict the degree of opening of the valve 14, and the fuel to be supplied to the burner 2 is reduced.

[0164] After both the initial value for determining the deterioration of ventilation and the initial sensor value are established by the initial value establishing unit 2027, the sensor fault determiner 2030 compares, at intervals, the output of the air flow sensor 16 which when no wind condition with the initial sensor value when no wind condition, while combustion at the burner 2 is not performed and the combustion fan 3 is not rotated. In other words, the fluctuation of the sensor output relative to the initial value is acquired. When the fluctuation value exceeds the sensor reference value provided in advance, it is assumed that a sensor fault has occurred, and a sensor fault signal is output.

[0165] The display means 2034 receives a ventilation deterioration warning signal from the ventilation deterioration determiner 2032, a danger warning signal for reporting the status of the lifetime of the appliance from the lifetime determiner 2031, and a sensor fault signal from the sensor fault determiner 2030, and then displays these signals on a display device for a remote controller, for example. Various display methods can be employed by the display means 2034: symbols, etc., having a variety of forms, for example, are displayed on a liquid crystal screen; a lamp ON/OFF or blinking state that is varied for visual notification; a changed volume of buzzer, a continuous sound, an intermittent sound, or the length of an intermittent sound. In the above structure, a signal from a fan rotation sensor 28 is used to determine whether the combustion fan 3 is not revolving or is revolving at the maximum revolution rate. A signal from a flame rod 20 is employed to determine whether or not combustion is taking place at the burner 2.

[Operational Sequence for Third Embodiment]

[0166] The processing of the thus structured embodiment will be specifically described while referring to the flow-charts in Figs. 23 and 24. In Fig. 23 is shown the processing performed by the initial value establishing unit 2027 for establishing the initial sensor output value when no wind condition, and the initial value for determining ventilation deterioration. This processing is performed at an appropriate time, such as when an appliance is powered on for an inspection after it is manufactured, when the appliance is installed and powered on, or when a command for the operation is issued by use of a command button to initiate an initial value establishment mode. In this processing, first, at step 2100, m = 0 is set. At step 2101, a check is performed to determine whether or not there is combustion at the burner 2. This checking is performed by detecting a signal from the flame rod 20. When there is no combustion at the burner 2, at step 2102 it is confirmed that the combustion fan 3 is halted.

[0167] Following this, at step 2103, the output of the air-flow rate sensor 16 is read. At step 2104, a check is performed to determine whether or not the reading of the sensor output has been terminated, i.e., whether or not T minutes has elapsed. The reading of the sensor output is performed, for example, one value each 0.1 second. At step 2104, a check is performed to determine whether or not T minutes have elapsed during which a predetermined number, such as five or ten, of sensor outputs have been read. When T minutes have elapsed, at step 2105, a calculation is performed to obtain the difference between the maximum value (MAX) and the minimum value (MIN) of the sensor outputs that were read. A check is then performed to determine whether or not the difference is disposed between the maximum value and the minimum value, i.e., the fluctuation of the fetched sensor outputs lies within the permissible range e₁ (e in Fig. 4 = e₁). If the fluctuation value is not within the permissible range, it is assumed that there is some wind condition. Since data, even if acquired, are affected by wind condition and can not serve as effective data, no data is fetched, and after a wait of 24 hours, the processing at step 2101 and the following steps are again performed.

[0168] When, at step 2105, it is ascertained that the difference between the maximum value and the minimum value lies within the limits of range e₁, the minimum value or the average value of the data sets that are read (the average value in this embodiment) is stored in the memory as V_MIN(m) (since m = 0 in this embodiment, V_MIN(0)). V_MIN(0) is one of the initial sensor values obtained when no wind condition.

[0169] At step 2107, with no combustion at the burner 2, the combustion fan 3 is rotated at the maximum revolution rate (3000 rpm in the embodiment) in the control range. At step 2108, the output of the air-flow rate sensor 16 is read.

[0170] In this case, a plurality of sensor output values are read, and at step 2109, a check is performed to determine whether or not the time for the reading has elapsed. When the time for the reading has elapsed, at step 2110, calculation is performed of a fluctuation between the maximum value and the minimum value from the sensor output values that were read, and a check is performed to determine whether or not the fluctuation lies within the permissible fluctuation range e₂ (e in Fig. 4 = e₂). When the fluctuation does not lie within the range e₂, it is assumed that data vary and that fluctuation occurs because there is some wind condition. No data are fetched, and after waiting 24 hours, the processing at step 2101 and the following steps is repeated. If, at step 2110, the difference between the maximum value and the minimum value lies within the permissible fluctuation range e₂, it is assumed that the condition is stable with no wind condition or wind. From the data sets that have been read, the maximum data value, or an average value (the average value in this embodiment), is stored in the memory as V_MAX(m) (since m = 0 in this case, V_MAX(0)). This is one of the initial values for determining whether deterioration of the ventilation has occurred.

[0171] At step 2112, a check is performed to determine whether or not m equals three. When the value of m is not yet three, at step 2114, m is incremented by one (in this embodiment m is increased from zero to one). At 2115, the operation is halted until one week has elapsed. Then, the processing at step 2102 and the following steps is performed. By repeating the operation at step 2101 and the following steps, the four initial sensor values V_MIN(0) through V_MIN(3), obtained while there is no wind condition, and the four initial values V_MAX(0) through V_MAX(3), for determining ventilation deterioration, are stored until m equals three.

[0172] When, at step 2112, it is ascertained that m = 3, at step 2113, the average of the four values V_MIN(0) through V_MIN(3) is calculated to establish the initial sensor value V_MIN for a condition whether there is no wind condition. Similarly, the average of the four V_MAX(0) through V_MAX(4) is calculated to establish the initial value V_MAX for determining whether there is ventilation deterioration when the combustion fan is being rotated at the maximum revolution rate. The established initial values V_MIN and V_MAX are stored in the memory 2028. The processing at steps 2100 through 2113 establishes the initial sensor value V_MIN, while no wind condition and no fan rotation immediately after the water heater is installed and when the ventilation in the water heater is not blocked; and the initial value V_MAX, a reference for determining whether there has been ventilation deterioration, while the combustion fan is rotated at the maximum revolution rate and ventilation is not blocked. These initial values are stored thereafter.

[0173] Fig. 24 is a flowchart for the processing whereby, after the initial value V_MAX and the initial sensor value V_MIN obtained during no wind condition have been established and stored, the deterioration of ventilation and the expiration of the lifetime of the appliance are determined at periodic intervals, e.g., every L combustion times or every M months. At step 2200, P = 0 and N = 0. Then, at step 2201, the process at steps 2101 through 2111 in the flowchart in Fig. 23 is performed. The sensor output V_MIN(N), which is obtained when the condition is stable with no wind condition and the combustion fan 3 is not rotated, and the sensor output V_MAX(N), which is obtained when the condition is stable with no wind condition and the combustion fan 3 is being rotated at the maximum revolution rate for the control range, are calculated and stored.

[0174] Following this, at step 2202, an absolute value of the difference between the initial sensor output value V_MIN when there is no wind condition, which is established and stored in advance, and V_MIN(N), which is obtained at step 2201, is acquired as a fluctuation value. The fluctuation value is compared with the sensor reference value that is provided in advance, i.e., permissible range for the air-flow rate sensor 16 in this embodiment, to determine whether or not the fluctuation value is within the permissible range. When the limits of the fluctuation lie outside the permissible range, at step 2209 it is ascertained that an air-flow rate sensor 16 is faulty. A sensor fault signal is then output by the sensor fault determiner 2030, and is displayed by the display means 2034. When the limits of the fluctuation lie within the permissible range, it is ascertained that the air-flow rate sensor 16 is operating normally, and program control moves to step 2203.

[0175] At step 2203, by employing the initial value V_MAX which was established and the value V_MAX(N) obtained at step 2201, for maintenance data when the combustion fan 3 is rotated at the maximum revolution rate with no combustion, the input down controller 2033 calculates a ratio for the value V_MAX(N) to the initial value V_MAX. A check is performed to determine whether or not the ratio is smaller than the reference ratio set in advance. Although the appropriate set value can be used as the reference ratio, in this embodiment, the reference ratio is set by using the graph data shown in Fig. 25.

[0176] In Fig. 25, V_A1 represents the output of the air-flow rate sensor 16 when the revolution rate for the combustion fan 3 is changed when no combustion. Data V_A1 is obtained at A₁, where the air flow passage area in the appliance is not blocked at all. Similarly, the relationship between the revolution rates and sensor outputs obtained when the blockage rate is changed at a plurality of stages, for example, 90%, 60%, 50% and 30%, is also separately calculated. The data V_A1 is obtained immediately after the appliance is manufactured and when there is absolutely no blockage of ventilation.

[0177] Graph data V_A2 represents the output of the air-flow rate sensor 16, immediately after the appliance was manufactured when there is combustion at the burner 2 and the fan revolution rate is changed, and when there is no ventilation blockage. Generally, compared with a period when there is no combustion, air flow resistance is increased when there is combustion. Thus, with respect to the normal output V_A1 at the time there is no combustion, the data of the fan revolution rate and the sensor output at the time there is no combustion and the passage area is reduced by Y % to the passage area A₂, is equivalent to the data for V_A2. Since the blockage rate Y% that corresponds to an increase in air flow resistance during combustion, relative to that when there is no combustion, is acquired as a well known value, the passage area A₂ at that time is also acquired as a well known value. Actually, therefore, the graph data V_A2 is obtained by calculation of graph data V_A1. The data V_A2 may be acquired when combustion is actually performed.

[0178] Graph data V_A4 represents the output of the air-flow rate sensor 16 under abnormal combustion conditions. Assuming that the blockage rate is changed to W% from the output V_A2 provided during normal combustion due to the deterioration by ventilation blockage, the data V_A4 is acquired from the data V_A1 or V_A2 by calculation. It should be noted that W% is calculated based on a case wherein the content of carbon monoxide in the exhaust exceeds a specified amount.

[0179] Data V_A3 represents the sensor output at an abnormal occasion when deterioration due to the blockage of ventilation has occurred. The data V_A3 is acquired from the above well known values V_A1, A₂ and A₄ by using the expression

. When the air flow passage area for the graph data V_A1 is assumed to be A₁, the blockage rate relative to the passage area A₁ differs for V_A2, V_A3 and V_A4. The passage area for the graph data V_A2 is A₂, the passage area for the graph data V_A3 is A₃, and the passage area for the graph data V_A4 is A₄.

[0180] In this embodiment, the ratio V_A3/V_A1, calculated for the abnormal sensor output V_A3 with no combustion to the normal sensor output V_A1 with no combustion is multiplied by constant K, and the result is employed as a reference rate. At step 2203, when the ratio of V_MAX(N) to V_MAX is equal to or greater than the reference rate, a problem in deterioration due to ventilation blockage does not arise, and combustion is preferably performed. Thus, combustion for the water heater is performed under normal combustion control.

[0181] When the ratio of V_MAX(N) to V_MAX is smaller than the reference rate, it is assumed that deterioration of the appliance has been caused by ventilation blockage. At step 2204, a check is performed to determine whether or not the revolution rate for the combustion fan 3 equals the maximum value of the control range. When the combustion fan revolution rate does not equal the maximum rate, it is assumed that the air-flow rate can be increased, even though deterioration due to the ventilation blockage has occurred, and a normal combustion operation is performed.

[0182] On the other hand, when the revolution rate for the combustion fan 3 equals the maximum rate (3000 rpm in this embodiment) in the control range, a "1" is added to P, and at step 2205 a check is performed to determine whether or not P = 2. Since P = 1 at this time, at step 2206, the input down controller 2033 reduces by X% the volume of gas to be supplied to the burner 2 and combustion is performed. At step 2207, the sampling unit 2025 uses the clock mechanism 2035 to determine whether or not the succeeding predetermined interval, for example, the time represented by L for combustion periods or M months, has elapsed. When the time has elapsed, at step 2208, N is incremented by one.

[0183] If it is ascertained at step 2205 that P = 2, at step 2211 a check is performed to determine whether or not deterioration of the appliance by ventilation blockage is complete. More specifically, a fluctuation between the initial value V_MAX for determining ventilation deterioration, which was established at step 2113 of the flowchart in Fig. 23, and the detected data (maintenance data) V_MAX(N) fetched at each interval at step 2201 is calculated by using the absolute value of the difference between V_MAX and V_MAX(N). Then, a check is performed to determine whether or not the fluctuation value is greater than the reference value D provided in advance. In this embodiment, the reference value D is provided as

. When the fluctuation value between the initial value and the maintenance data is not greater than reference value D, it is assumed that deterioration due to ventilation blockage has not occurred, and no warning signal is output. If the value of the fluctuation between the initial value and the maintenance data exceeds the reference value D, it is assumed that deterioration resulting from dust being deposited on a louver or on the curved faces of blades of the combustion fan 3, dust being attached to the burner 2, or soot blocking the water heater 8 has occurred, and at step 2212 a warning signal is output and is displayed on the display means 2034.

[0184] At step 2213, during combustion at the burner 2 of the water heater after the warning signal has been output, a check is performed to determine whether or not the fan revolution rate for the combustion fan 3 has reached the maximum revolution rate (upper limit) for the control range. When the fan revolution rate has not yet reached the upper limit, the fan revolution rate can be increased more, and combustion, therefore, is continued. When the fan revolution rate has exceeded the upper limit, it is assumed that deterioration due to the ventilation blockage is considered critical, and that expiration of the lifetime will occur, even though the revolution rate for the combustion fan is increased to the maximum. In this case, the lifetime determiner 2031 outputs a signal warning showing a danger that the expiration of the lifetime may occur. As the warning is displayed by the display means 2034, and combustion at the burner 2 is forcibly halted to disable any subsequent burner combustion, a dangerous condition resulting from incomplete combustion is avoided.

[0185] In the above embodiment, the setting standard requirement for the combustion fan has been established based on the maximum revolution rate in the control range for the combustion fan 3. The standard condition may be set based on a revolution rate that is slightly lower than the maximum revolution rate. Further, the setting standard requirement may be provided based on a drive current or the work performed by the combustion fan 3, instead of being based on the revolution rate.

[0186] In addition, in the above embodiment, the reference value D provided at step 2211 in the flowchart in fig. 24 may be calculated in advance and may be provided as externally input data. The appliance itself may acquire the data V_A1 in Fig. 25 by rotating the combustion fan 3, and may obtain the reference value D by computation and set it. A value other than

may be employed as the reference value D.

[0187] Moreover, in the above embodiment, to determine the deterioration due to ventilation blockage, as is shown in step 2211 in the flowchart in Fig. 24, the ventilation deterioration determiner 2032 calculates a fluctuation value by using an absolute value of a difference between the initial value V_MAX, for determining ventilation deterioration, and the maintenance data V_MAX(N). However, the fluctuation for determining the ventilation deterioration may be acquired by using an absolute value of a difference between the maintenance data V_MAX(N+1), which is fetched during the current interval, and the maintenance data V_MAX(N), which is fetched during the preceding interval, i.e., by using an absolute value for the fluctuation of the maintenance data that are fetched at the two intervals (corresponding to the inclination data changes). The ventilation deterioration determiner 2032 compares the fluctuation value with the reference value D and determines the extent of the deterioration due to ventilation blockage in the same manner as in the above embodiment. Thus, a case where the initial sensor value fluctuates in consonance with a transient change need not be taken into consideration. It is known from experience that ventilation blockage is normally accelerated. This is understood because incomplete combustion at a burner is begun by oxidization in the water heater, and much soot is generated accordingly, so that the ventilation blockage becomes worse. Therefore, no actual problem will arise when current data are compared with previously obtained data.

[0188] The condition determiner in the above embodiment determines the wind condition by using a data variance detected by the air supply volume sensor (the air-flow rate sensor 16). However, another determination method may be employed whereby the revolution rate for the combustion fan 3 is controlled so as to maintain a steady output by the air-flow rate sensor. When the fluctuation of the fan revolution rates detected by a fan revolution sensor lies within the permissible fluctuation range, it is assumed that there is no wind condition, but when the fluctuation exceeds the permissible range, it is assumed that there is some wind condition. In this case, a fan drive current or a work amount may be detected instead of the fan revolution rate, and the wind condition may be identified by determining whether or not a variance in the detected data lies within the permissible fluctuation range.

[0189] As is described above, when the wind condition is determined by using a driving condition variable, such as a fan revolution rate, the deterioration due to ventilation blockage can be determined from the magnitude of the variation in the driving requirements, such as the fan revolution rate. The driving condition, such as the fan revolution rate for which the output of the air-flow rate sensor serves as a set value, when there is no deterioration due to ventilation blockage, is set as an initial value. At predetermined intervals, the driving condition, such as a fan revolution rate for which the outputs by the air-flow rate sensor are the same, is obtained. When a value for a fluctuation difference between the fan driving condition detected at each interval and the initial value, or a value for a fluctuation difference between the fan driving condition acquired at the current interval and the fan driving condition acquired at the preceding interval exceeds the reference value, it is assumed that deterioration has occurred due to ventilation blockage.

[0190] According to the third embodiment, the initial sensor value when there is no wind condition, deterioration due to ventilation blockage does not occur and the combustion fan is halted, and the initial value for determining ventilation deterioration when the combustion fan is rotated under the standard requirements, are established in advance as data acquired when no combustion, and are stored. The deterioration due to ventilation blockage is detected in consonance with the fluctuation relative to the initial value for the maintenance data that are fetched at predetermined intervals. Therefore, the initial value of the air-flow rate sensor whose characteristic varies for each combustion appliance is established not at shipping time, but in consonance with the environment after the appliance has been installed. Therefore, the expiration of a lifetime due to deterioration by ventilation blockage can be precisely determined.

[0191] In addition, according to the third embodiment, since the data for the air-flow rate sensor when the combustion fan is halted are fetched at set intervals, the fluctuation relative to the initial sensor value during no wind condition is calculated to determine sensor faults. Since the value output by a faulty sensor is not adopted as an effective value, the determination of deterioration due to ventilation blockage and the reliability of that processing can be enhanced.

[Fourth Embodiment]

[0192] In the third embodiment, when the output of the air-flow rate sensor 16 during no wind condition is changed from the initial value outside a permissible range, it is ascertained that the air-flow rate sensor is faulty. However, even when the zero point fluctuates, some air-flow rate sensors can be continuously used if correcting the zero point at the initial value by adding the fluctuation value. The feature of the fourth embodiment is that the zero point value, which is an output value for the air-flow rate sensor 16 when no wind condition, is detected and corrected for.

[0193] Fig. 26 is a detailed flowchart for detecting the zero point value. In the example processing in Fig. 26, zero point correction is performed when the appliance is activated while it is cool.

[0194] As is shown in Fig. 26, when a hot water valve is opened and the flow rate sensor is activated, first, as initial values, a "0" is set for the output count m for an inappropriate data signal, and a "0" is also set for the maximum output value V_omax and the minimum value V_omin of the air-flow rate sensor 16.

[0195] At step 3001, the value V_o output by the air-flow rate sensor 16 is stored in the memory.

[0196] At step 3002, the value V_o output by the air-flow rate sensor 16 stored in the memory is compared with the upper output limit value V_omaxlimit at the zero point stored in the memory, and with the lower output value V_ominlimit at the zero point.

[0197] At steps 3003 and 3004, if the output value V_o is equal to or less than the zero point upper output limit value V_omaxlimit, and is equal to or greater than the zero point lower output value V_ominlimit, the value V_o output by the air-flow rate sensor 16 is sequentially transmitted as stored data V_o,i to the memory 30.

[0198] At step 3002, if the output value V_o is equal to or greater than the zero point upper output limit value V_omaxlimit, or is equal to or less than the zero point lower output value V_ominlimit, the sensor output value V_o is regarded as inappropriate data and is erased from the memory. At step 3013, the output count for an inappropriate data signal is stored in the memory.

[0199] At steps 3005 and 3006, the sensor output value V_o,i stored in the memory for use is regarded as the maximum value V_omax, and is compared with the data V_o,i, which is used next. The larger value is stored in the memory as the maximum value V_omax. In this manner, the maximum value V_omax is selected from the sensor outputs V_o,i that are sequentially used at step 3002.

[0200] At steps 3007 and 3008, in the same manner as above, the minimum value V_omin is selected from the sensor outputs V_o,i.

[0201] At step 3009, a difference between the maximum value V_omax and the minimum value V_omin is calculated as needed, and the difference is compared with a permissible fluctuation range e. When the difference is equal to or exceeds the permissible range e, it is assumed that there is some external wind condition. The detected data is regarded as inappropriate data, and the sensor output is read again. If the difference lies within the fluctuation range, it is assumed that there is no wind condition, and the detected data is stored in the memory as appropriate data.

[0202] At step 3010, a check is performed to determine whether or not the number of the sensor output values V_o,i stored in the memory as appropriate data obtained when no wind condition, has increased until it equals a predetermined number t. When the number of the sensor output values V_o,i equals to the predetermined number t, the sensor output values V_o,i are employed as correction data.

[0203] At step 3011, the average value for the correction data is calculated, and is stored in the memory as zero point correction value V_o of the air-flow rate sensor 16. The average value is to be used for determining the expiration of a lifetime and for controlling an air-flow rate.

[0204] When, at steps 3002 or 3009, it is ascertained that the detected data is regarded as inappropriate data, at step 3014, count m for the detected data regarded as inappropriate data is compared with a predetermined count M. When m < M, at step 3016, V_o,i is reset, and the detection of the sensor output at step 3000 and the following steps is performed. When

, it is assumed that an appropriate zero point can not be detected and an error signal is output. The zero point correction is thereafter terminated. In this case, zero point correction process is again performed after a predetermined period of time has elapsed. When an error signal is output frequently, it can be assumed that the air-flow rate sensor 16 is faulty or that its lifetime has expired.

[0205] At step 3012, as a result of the correction process, the zero point value is used as a new corrected zero point for the air-flow rate sensor, and program control moves to a post-fan ignition sequence to begin a normal combustion operation by using the air-flow rate sensor.

[0206] The present invention is not limited to the first through the fourth embodiments, and can be modified in various modes. For example, although in the above embodiments, the burner 2 that has three stages for switching a combustion function has been employed, the number of stages for the combustion function of the burner 2 may be a number other than three, or a burner may be used that is not a combustion switching type.

[0207] In the above embodiments, a differential pressure at an interval between the upper portion and the lower portion, with the burner 2 in between, has been detected by the differential pressure sensor 16, which is an air-flow rate sensor. A differential pressure need only be detected at a desirable segment in the path between the upstream and the downstream portions in the air-flow rate passage, which extends from the air supply section for the burner to an exhaust path. Besides the above described segment, a number of segments in the path for detecting a differential pressure can be set, such as a segment between the inlet port for a combustion fan and a combustion chamber, a segment between the outlet for the combustion fan and the combustion chamber, a segment between the air inlet or the air outlet for the combustion fan and an upper exhaust tap of a water heater, or a segment between a combustion chamber and an exhaust tap. However, in the structure shown in this embodiment, wherein the differential pressure is detected at a segment in the path between the upper and the lower portions, with the burner 2 in between, since the blockage of the burner 2 with dust, etc., seldom occurs relative to the water heater and there is almost no transient change in air flow resistance at the burner 2, the air flow driven by the combustion fan 3 can be detected precisely by using a differential pressure. For this reason, the system employed for the embodiments, where the differential pressure is detected at a segment in the path between the upstream and downstream portions with the burner 2 in between, is preferable.

[0208] In the above embodiments, the differential pressure sensor 16 has been employed as an air-flow rate sensor. Instead of the differential pressure sensor 16, various other sensors for detecting an air-flow rate directly or indirectly may be employed, such as a hot-wire anemometer or a Karman vortex anemometer, or an anemometer of a propeller rotation type for detecting an air-flow rate directly.

[0209] Further, in the above embodiments, the setting condition for a combustion fan has been provided based on a fan revolution rate. The setting condition for the combustion fan may be provided based on another condition, such as a drive current for the combustion fan or the amount of work performed. In this case, the combustion fan is rotated in accordance with the setting condition, such as a fan driving current or the amount of work performed, and determination for an occurrence of an abnormality or the expiration of the lifetime of an appliance is performed by comparing a detected air-flow rate with a reference air-flow rate.

[0210] The determination for the wind condition has been performed by monitoring to determine whether the output of the air-flow rate sensor varies. However, during the rotation of the combustion fan, the fan revolution rate is sometimes adjusted so as to maintain a steady output for the air-flow rate sensor. In such a case, the wind condition can be detected by monitoring to determine whether the fan revolution rate is varied. The same procedure is employed for monitoring the power of the combustion fan.

[0211] In addition, the determination of the expiration of a lifetime or of an occurrence of an abnormality can be performed by monitoring to ascertain whether the combustion fan is revolving at a required revolution rate or greater, or by monitoring to ascertain whether or not only the output of the air-flow rate sensor is less than is necessary.

[0212] Furthermore, in the above embodiments, a single-function water heater (a water heater with only a hot water supply function) has been employed as a combustion appliance. The present invention, however, can be applied to compound water heaters having both a hot water supply function and a supplementary bathtub heating function, or both a hot water supply function and a hydronic heating function, to combustion appliances having a variety of burners, such as bath water heaters, space heating appliances, space cooling appliances, space heating and cooling appliances, and to air conditioners.

[0213] Moreover, although the combustion fan 3 of a draft forcing type has been employed in the above embodiments, a combustion fan 3 of a draft induction type may be employed.

INDUSTRIOUS USABILITY

[0214] As is described above, a combustion appliance according to the present invention can control combustion by maintaining a low carbon monoxide, hydrocarbon and nitrogen oxide exhaust content, and can prevent in advance the occurrence of incomplete combustion due to a blockage of the appliance with soot, or an unexpected plugging of an outlet port.

[0215] Further, according to the present invention, in order to prevent incomplete combustion in advance, the relationship between the air-flow rate and the combustion fan revolutions is examined to determine whether or not it is within a normal range. At this time, the output of the air-flow rate sensor, or the fan revolution rate is monitored whether there is no external wind condition. Since the determination can be performed without being affected by external conditions, undesirable fault determinations are prevented.

[0216] In addition, according to the present invention, the relationship between the air-flow rate and the revolution rate for the combustion fan is monitored. When the relationship is shifted from the normal condition to a first range, first, the gas volume supplied to the combustion burner is reduced and an input down operation is performed. If the relationship between the air-flow rate and the revolution rate for the combustion fan is shifted from the normal condition to a second range, it is assumed that the lifetime of the combustion appliance has expired, and combustion is halted. Therefore, unnecessary repair or disposal of a combustion appliance is eliminated.

[0217] Furthermore, according to the present invention, since the initial value for the air-flow rate sensor is detected first, the value output by the air-flow rate sensor, which varies depending on the product and the installation environment, can be used appropriately.

[0218] Moreover, according to the present invention, zero point correction is performed by using the value output by the air-flow rate sensor that is detected when there is no wind condition, so that a barrier due to a transient change of the sensor can be removed.

Claims

1. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for determining there is no outside wind condition when a change in said air-flow rate, detected by said air-flow rate sensor during no revolutions or when a constant revolution rate of said combustion fan, is within a predetermined permissible range.

2. A combustion appliance according to claim 1, wherein, when said air-flow rate, detected by said air-flow rate sensor while said combustion fan is not revolving or is revolving at said constant revolution rate, is maintained within a predetermined range for a predetermined period of time, said controller detects that said fluctuation in said air-flow rate is within said predetermined permissible range.

3. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate of said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for determining there is no outside wind condition when a change in said revolution rate, detected by said revolution rate detector during said combustion fan being so rotated that said air-flow rate detected by said air-flow rate sensor is maintained to a constant value, falls within a predetermined range.

4. A combustion appliance according to claim 3, wherein, when said revolution rate, detected by said revolution rate detector while said combustion fan is so rotated that the air-flow rate detected by said air-flow rate sensor is maintained to the constant value, is maintained within a predetermined range for a predetermined period of time, said controller detects that said fluctuation in said revolution rate is within said predetermined permissible range.

5. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for storing a reference air-flow rate for determining whether an abnormality or expiration of a lifetime has occurred during said combustion fan being rotated at a predetermined revolution rate, for determining there is no wind condition when a change in said air-flow rate, detected by said air-flow rate sensor during no revolutions or a constant revolution rate by said combustion fan, is within a predetermined permissible range, and for determining an abnormality or an expiration of a lifetime has occurred when said air-flow rate, detected by said air-flow rate sensor during said predetermined revolution rate of said combustion fan and no wind condition being detected, is lower than said reference air-flow rate.

6. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate for said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for storing a reference revolution rate for determining whether an abnormality or expiration of a lifetime has occurred during said combustion fan being so rotated that a constant air-flow rate is detected by said air flow sensor, for determining there is no wind condition when a change in said revolution rate, detected by said revolution rate detector during said combustion fan being so rotated that a certain constant air-flow rate is detected by said air-flow rate sensor, is within a predetermined permissible range, and for determining an abnormality or expiration of a lifetime has occurred when said revolution rate, detected by said revolution rate detector during said combustion fan being so rotated that said constant air-flow rate is detected by said air-flow rate sensor, is higher than said reference revolution rate.

7. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for storing a reference air-flow rate to determine whether an abnormality or expiration of a lifetime has occurred when said combustion fan is revolving at a predetermined revolution rate, and for determining an abnormality or expiration of a lifetime has occurred when a change in said air-flow rate, detected by said air-flow rate sensor during said combustion fan being revolving at said predetermined revolution rate, is within a predetermined permissible range, and when said air-flow rate detected by said air-flow rate sensor is lower than said reference air-flow rate.

8. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate for said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for storing a reference revolution rate to determine whether an abnormality or expiration of a lifetime has occurred when said combustion fan is so rotated that a constant air-flow rate is detected by said air-flow rate sensor, for determining an abnormality or expiration of a lifetime has occurred when a change in said revolution rate, detected by said revolution rate detector during said combustion fan being revolving so that said constant air-flow rate is detected by said air-flow rate sensor, is within a predetermined permissible range, and when said revolution rate detected by said revolution detector is higher than said reference revolution rate.

9. A combustion appliance according to claim 5 or 7,
   further comprising a fuel controller for feeding sufficient fuel to said burner to supply a required caloric value,
   wherein, when said abnormality or said expiration of said lifetime is detected, said supply of said fuel to said burner is forcibly reduced by said fuel controller.

10. A combustion appliance according to claim 9, wherein said reference air-flow rate includes a first reference air-flow rate and a second reference air-flow rate lower than said first reference air-flow rate;

when said abnormality or said expiration of said lifetime is detected, and when said air-flow rate detected by said air flow sensor is lower than said first reference air-flow rate, said supply of said fuel to said burner is forcibly reduced by said fuel controller;

and when said air-flow rate detected by said air-flow rate is lower than said second reference air-flow rate, said supply of said fuel to said burner is halted by said fuel controller.

11. A combustion appliance according to claim 6 or 8, further comprising:

a fuel controller for providing an adequate supply of fuel to said burner to maintain a required caloric value,
   wherein when said abnormality or said expiration of said lifetime is detected, said supply of said fuel to said burner is forcibly reduced by said fuel controller.

12. A combustion appliance according to claim 11, wherein said reference revolution rate includes a first reference revolution rate, and a second reference revolution rate higher than said first reference revolution rate;

when said abnormality or said expiration of said lifetime is detected, and when said revolution rate detected by said revolution rate detector is higher than said first reference revolution rate, said supply of said fuel to said burner is forcibly reduced by said fuel controller;

and when said revolution rate detected by said revolution rate detector is higher than said second reference revolution rate, said supply of said fuel to said burner is halted by said fuel controller.

13. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for detecting an absence of wind condition when a change in said air-flow rate, detected by said air-flow rate sensor while said combustion fan is not revolving or is revolving at a constant revolution rate, is within a predetermined permissible range, for storing, as an initial value, said air-flow rate detected by said air-flow rate sensor while said combustion fan is revolving at a predetermined revolution rate at the time, and for detecting a deterioration in ventilation, after a predetermined time since said initial value being stored, when said absence of wind condition is detected and when said air-flow rate, detected by said air-flow rate sensor while said combustion fan is revolving at said predetermined revolution rate, is changed from said initial value by an amount that is equivalent to or greater than a reference value.

14. A combustion appliance according to claim 7, wherein, when a difference between said air-flow rates detected by said air-flow rate sensor before and after said predetermined time has elapsed, is equal to or greater than said reference value, said controller detects that ventilation deterioration has occurred.

15. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate for said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for detecting an absence of wind condition when a change in a revolution rate, detected by said revolution rate detector while said combustion fan is so revolving that a constant reference air-flow rate is detected by said air-flow rate sensor, is within a predetermined permissible range, and storing, as an initial value, said revolution rate detected by said revolution detector at the time, and for detecting a deterioration in ventilation, after a predetermined time since said initial value being stored, when said absence of wind condition is detected and when said revolution rate by said revolution rate detector is changed from said initial value by an amount that is equivalent to or greater than a reference value.

16. A combustion appliance according to claim 15, wherein, when a difference between said revolution rates detected by said revolution rate detector before and after the predetermined time has elapsed, is equal to greater than said reference value, said controller detects that ventilation deterioration has occurred.

17. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to and discharging air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route extending from an inlet path for said burner to an outlet path;

a heat exchanger, located along said air flow route, supplied with a calorific value by the burner, and connected to an input pipe along which a heat medium is supplied, and to an outlet pipe along which said heat medium is transmitted;

a fuel controller for supplying, to said burner, fuel required for maintaining at a set temperature said heat medium transmitted along said outlet pipe;

a fan controller for rotating said combustion fan so as to maintain an appropriate air-flow rate for burning said fuel by said burner; and

a controller for storing a reference air-flow rate for determining whether an abnormality or expiration of a lifetime has occurred while said combustion fan is rotated at a predetermined revolution rate, for determining there is no wind condition when a change in said air-flow rate, detected by said air-flow rate sensor while there are no revolutions or a constant revolution rate of said combustion fan, is within a predetermined permissible range, and for determining an abnormality or an expiration of a lifetime has occurred when said air-flow rate, detected by said air-flow rate sensor during said predetermined revolution rate of said combustion fan and no wind condition being detected, is lower than said reference air-flow rate.

18. A combustion appliance comprising:

a burner;

a revolution rate detector for detecting a revolution rate for said combustion fan;

a combustion fan for supplying air to and discharging air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route extending from an inlet path for said burner to an outlet path;

a heat exchanger, located along said air flow route, supplied with a calorific value by the burner and connected to an input pipe along which a heat medium is supplied, and to an outlet pipe along which said heat medium is transmitted;

a fuel controller for supplying, to said burner, fuel required for maintaining at a set temperature said heat medium transmitted along said outlet pipe;

a fan controller for rotating said combustion fan so as to maintain an appropriate air-flow rate for burning said fuel by said burner; and

a controller for storing a reference revolution rate for determining whether an abnormality or expiration of a lifetime has occurred during said combustion fan being so rotated so that a constant air-flow rate is detected by said air-flow rate sensor, for determining an abnormality or expiration of a lifetime has occurred when a change in said revolution rate, detected by said revolution rate detector during said combustion fan being revolving so that said constant air-flow rate is detected by said air-flow rate sensor, is within a predetermined permissible range, and when said revolution rate detected by said revolution detector is higher than said reference revolution rate.

19. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate of said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for detecting an absence of wind condition when a change in said air-flow rate, detected by said air-flow rate sensor while said combustion fan is not revolving, is within a predetermined permissible range, and for storing, as a zero point, said air-flow rate detected by air-flow rate sensor when said absence of wind condition is detected.

20. A combustion appliance comprising:

a burner;

a revolution rate detector for detecting a revolution rate of said combustion fan;

a combustion fan for supplying air to and discharging air from said burner;

an air-flow rate sensor for detecting an air-flow rate along an air flow route extending from an inlet path for said burner to an outlet path;

a heat exchanger, located along said air flow route, supplied with a calorific value, and connected to an input pipe along which a heat medium is supplied, and to an outlet pipe along which said heat medium is transmitted;

a fuel controller for supplying, to said burner, fuel required for maintaining at a set temperature said heat medium transmitted along said outlet pipe; and

a fan controller for rotating said combustion fan so as to maintain an appropriate air-flow rate for burning said fuel by said burner; and

a controller for detecting an absence of wind condition when a change in said air-flow rate, detected by said air-flow rate sensor while said combustion fan is not revolving, is within a predetermined permissible range, and for storing said air-flow rate detected by said air-flow rate sensor while said condition during which there is no wind condition is detected.

21. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate for said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for storing a reference air-flow rate for determining whether an abnormality or an expiration of a lifetime occurs while said combustion fan is revolving at a predetermined revolution rate, and for determining said abnormality or said expiration of said lifetime has occurred when said air-flow rate, detected by said air-flow rate sensor, while said combustion fan is revolving at said predetermined revolution rate, is continuously lower than said reference air-flow rate for a predetermined period of time.

22. A combustion appliance comprising:

a burner;

a combustion fan for supplying air to, and exhausting air from said burner;

a revolution rate detector for detecting a revolution rate for said combustion fan;

an air-flow rate sensor for detecting an air-flow rate along an air flow route from an air supply path to an air exhaust path for said burner; and

a controller for storing a reference revolution rate for determining whether an abnormality or an expiration of a lifetime occurs while said combustion fan is so revolving that a constant air-flow rate is detected by said air flow sensor, and for determining said abnormality or said expiration of said lifetime occurred when said revolution rate, detected by said revolution rate detector while said combustion fan is so revolving that said constant air-flow rate is detected by said air-flow rate sensor, is continuously higher than said reference revolution rate for a predetermined period of time.

Drawing