| 摘要 |
PURPOSE:To prevent water from being boiled due to opeated ooerations at the time of a disconnection and prevent an erroneous operation of a disconnection-detecting circuit from occuring at the time of an extreme fall of temperature, by a method werein a detection level of a disconnection-detecting operation is changed for a predetermined period of time after the start of combustion in a water heater so that the disconnection can be detected even in the predetermined period of time. CONSTITUTION:When the hot water temperature is low, a comparator 12 generates an output ''1'', whereby a burner motor driving circuit 15 is turned ON, charging of a capacitor 17 is simultaneously started, a combustion-controlling ciruit 19 is turned ON, and combustion is started. In addition, charging of a capacitor 21 is started, at which moment a transistor 10 is in an OFF condition. Accordingly, the disconnection-detecting circuit 13 is not operated unless the resistance value of a thermistor 2 becomes extremely high, so that a normal operation is retained even when the temperature is lowered to 0 deg.C. When charging of the capacitor 21 proceeds to reach a voltage higher than a threshold valvue of a circuit 23, a transistor 10 is turned ON, and the detection level is changed to a normal set level. When a disconnection occurs in a thermistor 2, the output of the camparator 13 becomes ''1'' because the potential at a point (a) is 0V, so that a signal is fed to a safety circuit 24, a contact 25 is opened, and the combustion operation is stopped. |
