A heating system for motor vehicles

A heating system for motor vehicles with a water-cooled internal combustion engine, which heating system has a heat exchanger (11) which is acted on by the cooling water circuit of the internal combustion engine (10) on the one hand and by an auxiliary heating unit (14) which is independent of the internal combustion engine (10) on the other. A thermostatically activated switching element (17) causes the hot water to flow via the heat exchanger (11) below a temperature prescribed by the thermostat (35), when the auxiliary heating unit (14) is switched on, and to flow additionally via the internal combustion engine (10) above this temperature. The switching element (17) also causes the engine cooling water to flow via the heat exchanger (11) when the auxiliary heating unit (14) is switched off. A non-return valve (30) blocks flow in the direction from an outflow chamber (34) to an inflow chamber (25). The inflow chamber (25) and outflow chamber (34) are connected to one bother via at least one leakage hole (29). The thermostat (35) is arranged in the inflow chamber (25) and provided with an activation element (38) which opens the non-return valve (30) above a prescribed temperature in the inflow chamber (25) and thus enables the through-flow from the outflow chamber (34) to the inflow chamber (25). Hot water heated up by the unit (14) thereby flows through engine (10) via the cooling water circuit in order to heat up the engine (10).