PURPOSE: To decrease energy consumption to prevent freeze, by transferring the heat of the motor part of a circulating pump, which intervense to a heating circuit, to a hot water supply circuit.

CONSTITUTION: An inner fluid is circulated through a system, consisting of a cistern 8, a circulating pump 8, directional control valves V2, V4, and V5, a heat exchanger 9 for heating, a radiator 11, and coming back to the top cistern 8, during a heating time, and heating by radiating heat from a radiator 11 is taken place. On the other hand, in a freeze preventing time, when burners 2a and 9a are extinguished and a bypass valve 12 is opened, the inner fluid is circulated through a system, consisting of a cistern 8, a circulating pump 7, a directional control valve V1, a heat exchanger pipe 16, a directional control valve V5, a heat exchanger 9 for heating, a bypass valve 12, and coming back to the top cistern 8. During this time, the temperature of an inner fluid can be risen by absorbing the heat from a motor part 14 of the circulating pump 7, accordingly, the temperature of water in a water feed pipe 3a and a water supply tank 3 is kept high, as well, so that the heating apparatus is prevented from ffreezing.