To improve a durable service life by preventing elongation of driving time of a solenoid excessive pressure relief valve in a water heater with a heating function provided with a heat exchanger of a system provided with both a heat exchanger for hot water supply and a heat exchanger for heating, and using the same burner for heating.

Since the heat exchanger 20 for heating and the heat exchanger 7 for hot water supply are heated during heating operation, by providing a control means 27 for opening the solenoid excessive pressure relief valve 26, releasing pressure to a heating circuit 24, and closing the solenoid excessive pressure relief valve 26 when using heating and hot water supply at the same time, the driving time of the solenoid excessive pressure relief valve 26 is shortened, and the durable service life is improved.