PURPOSE: To permit to supply water to a heat collector as well as pressurized hot-water supply to water utilizing parts with one set of pump by a method wherein the pump and a normally open type opening and closing valve are provided in a water sending pipe between a heat accumulating tank and a heat collector and a hot-water supplying pipe is connected to said water sending pipe.

CONSTITUTION: The water sending pipe 16, connecting the heat accumulating tank 14 and the heat collector 12, is provided with the pump 17 and the opening and closing valve 18 while the hot-water supplying pipe 21 is connected to said water sending pipe 16. When a pressure at the downstream side of a non-return valve 24 becomes lower than a predetermined pressure by supplying hot-water, a pressure switch 25 detects it, the pump 17 is operated and the pressurized hot-water supply is continued. On the other hand, the opening closing valve 18 is conducted and closed, therefore, the total output of the pump 17 is utilized for the supply of hot-water. Thereafter, when a hot-water supplying port 23 is closed and the supply of hot-water is stopped, the pump 17 is stopped and the opening and closing valve 18 is opened. Thus, supply of water to the heat collector 12 and the pressurized hot-water supply may be effected by one set of the pump 17.