| 摘要 |
PURPOSE:To prevent the freezing accident of a heat exchanger of a water heater by igniting a burner with a minimum ability on the basis of signal from a freeze sensor, and extinguishing fire on the basis of a signal from a hot water feed temperature detector. CONSTITUTION:A freeze sensor 6 provided in a feed water pipe 5 of a heat exchanger 1 of the water heater detects a feed water teperature and a tempera ture in the vicinity of the feed water pipe 5. A hot water feed pipe 8 is provided with a hot water feed temperature detector 10 in the vicinity of the heat exchanger 1. When a freeze detected temperature Tc of a freeze sensor 6 reaches a freeze preventive set temperature TcON at a time t0 freeze preventing control means 12 actuates a combustion control circuit 13 and sets an ability setter 14 at a minimum combustion quantity to ignite a burner2. The hot water feed temperature T reaches a set temperature T at a time t1, and the combus tion is stopped. By the stop of the combustion, the hot water feed temperature T0 is lowered, and at a time t2, it reaches again a combustion operating tempera ture TON. By repeating the operation, when the detected temperature Tc reaches a freeze prevention release temperature Tc OFF at a time t4, the freeze preven tive operation is stopped.
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