Additional water heating device for an automotive vehicle

The auxiliary water heater (30) is for a vehicle (10), the engine (14) of which has a coolant circuit (16) with a cooling unit (18, 20, 22). The cooling unit can be coupled to a heating circuit (26) of the water heater, so that the water heater will not be heating water while the engine is being cooled. The heater is arranged to that the serviceability of the cooling unit is reported and switch off and on as required.