A door lock for a washing machine or drier includes a support casing (2) which is adapted to be fixed to the machine. The casing (2) contains a control and timing device with a resistive heater element, an electrical switch with a bistable resilient blade operated by a locking slide (4) which is movable relative to the casing (2), and a sensor for sensing the water level in the washing chamber to keep the door closed when the level exceeds a predetermined value.