| 摘要 |
PURPOSE:To ensure safe operation of a hot water feeder even at the time when freezing of water or trouble of a thermistor is caused, by applying a thermistor voltage and a partial voltage of the thermistor and a resistance connected in series thereto to a voltage comparator of a circuit for detecting the temperature of hot water when freezing of water in the hot-water supply pipings is caused. CONSTITUTION:A voltage divided by resistors 3, 6 out of resistors 3, 4, 5, 6 connected respectively to one input terminals of voltage comparators 7, 8, 9, is applied to the voltage comparator 9, which produces a ''low'' output when a thermistor 2 detects 0 deg.C at which freezing of water is caused. Therefore, when is frozen, a transistor 15 is turned OFF and a safety solenoid valve 21 is closed, so that combustion is stopped. Further, if some trouble is caused with the thermistor 2 when the valve 21 is opened, combustion is also stopped since the value of resistance becomes infinite. Thus, it is enabled to prevent waterless heating of a boiler or other troubles even when freezing of water or trouble of the thermistor is caused, and hence to ensure safe operation of the hot water feeder. |
