A burner having an air regulator upstream of the burner which automatically controls the air pressure at the inlet of the burner at a fixed value. The air regulator comprises a container (2) divided into a zone (6) in communication with the combustion chamber and another zone (5) in communication with the air supply to the burner, the zones (5, 6) being separated by a moveable partition (3) connected to a regulating device (1) for regulating the amount of air supply entering the burner form the atmosphere. When the moveable partition (3) moves in response to a pressure difference between the zones (5, 6) there is change in the amount of air supplied to the burner.