GAS HEAT SOURCE MACHINE

PROBLEM TO BE SOLVED: To provide a gas heat source machine which can operate for a long time even if electric power from a commercial power source is cut off and electric power from an auxiliary power source of limited capacity is used instead.SOLUTION: A gas heat source machine 1 includes a blower fan 14 supplying oxygen-containing gas for combustion and a heat exchanger 12 heating fed water at a combustion section 11 including a gas burner 13, further includes a combustion control part 10 controlling a fuel gas supply amount and a blower fan rotational speed based upon an input relation index in response to a hot water supply amount and a hot water temperature which are requested, and usually receives electric power from an external AC power source 8. In a power cutoff state where electric power from the external AC power source 8 is cut off, the gas heat source machine further includes an auxiliary power supply receiving means 5 and an auxiliary power supply reception detection means of detecting an auxiliary power supply reception state and in an auxiliary power supply reception state, the combustion control part 10 controls combustion in the combustion section 11 within a power-saving input region in which an input relation index is satisfied and an electric power consumption by the blower fan 14 is small.