| 摘要 |
PROBLEM TO BE SOLVED: To prevent city water in a heat exchanger for hot water supply from freezing without requiring an electric heater having heat generation rate by operating a hot water supply burner during extra firing and supplying a bathtub with hot water for filling. SOLUTION: When a predetermined waiting time elapses before flow rate of city water in a hot water supply passage 13 detected by a flow rate sensor 15a reaches a specified hot water supply working level, process is ended by closing a hot water filling valve 14 without operating a hot water supply burner 23a. Upon elapsing an appropriate time, a decision is made whether extra firing operation is progress or not and anti-freeze control of a heat exchanger for hot water supply is repeated. According to the method, even if chill is fed to the heat exchanger for hot water supply 23 by means of a fan during extra firing operation, the hot water supply burner 23a is operated and city water in the heat exchanger for hot water supply 23 is prevented from freezing.
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