Device for the heating of the passenger compartment of a motor vehicle

The heater for a motor vehicle passenger compartment has a casing (1) in which cooling water can circulate. A heater (6,7,9) is connected to a reservoir (5) and heats the water by convection through the casing wall. The heater has controls (11,15) which supply power to the heater element in response to a control signal (Vcc). The controls have a regulator (13) to allow a gradual transition between heating stages.