To improve an antifreezing function of a water heater in the cold.
The water heater 2, which comprises a primary heat exchanger 30 for absorbing sensible heat of combustion exhaust and a secondary heat exchanger 32 for absorbing latent heat of the combustion exhaust, is provided with a temperature detection means (temperature sensors 118 and 120) for detecting antifreezing temperature, a combustion means (burner group 40) for supplying combustion exhaust generated by combustion to the primary heat exchanger and secondary heat exchanger, an air supply means for supplying air to the combustion means, and a control means (controller 138) for causing the combustion means to combust and driving the air supply means according to the detection temperature of the temperature detection means. When the temperature detection means detects the antifreezing temperature, the combustion means is caused to combust for a fixed time to heat the primary heat exchanger, and the air supply means is driven for a fixed time after the combustion stop of the combustion means to lead air from the primary heat exchanger to the secondary heat exchanger such that remaining heat in the primary heat exchanger heats the secondary heat exchanger.
YAMASHITA RYOJI
NAITO KATSUMI
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