| 摘要 |
PROBLEM TO BE SOLVED: To regularly keep hot water at a high temperature close to the boiling point with a simple circuit structure by switching the heat retaining temperature according to the operation quantity of current carrying or interruption of a heating means for a prescribed time, and controlling the current carrying to the heating means so as to keep the hot water temperature at this switched heat retaining temperature to perform the heat retaining operation. SOLUTION: A control means 6 calculates and sets the heat retaining temperature from the hot water temperature in water boiling. When a heat retaining operation is started without boiling water after input of a power source, the current carrying to a heat retaining heater 3 is controlling so as to keep the hot water temperature at a preset prescribed heat retaining temperature to perform the heat retaining operation, and a time clocking is also performed by a timer means 15. On this time clocking, the heat retaining temperature is switched according to the operation quantity of current carrying or interruption of the heat retaining heater 3 for a prescribed time. More specifically, the heat retaining temperature is successively switched until the operation quantity reaches a prescribed quantity, and the current carrying to the heat retaining heater 3 is controlled so as to keep the hot water temperature at the switched heat retaining temperature to perform the heat retaining operation.
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