JP2870186B

PURPOSE:To prevent freezing from happening by estimating the outside air temperature by the temperature decrease of a water passage by a method wherein while the operation is stopped, the difference in temperature of a water passage which is detected by a temperature detecting means, is compared with the descending temperature and the outside air temperature, which are previously stored, by a calculation memory means, and the outside air temperature is retrieved by this function. CONSTITUTION:The operation flow of a control device 11 decides whether a burner 8 is operating or not by a signal of a frame rod 12, and when the burner 8 stops, the operation flow of the control device 11 decides whether water is running or not. When the burner 8 is operating and the water is running, a hot water supply machine is running, and freezing does not take place, and the flow of operation returns to the original. When the burner 8 is not operated, and the water is also not running, i.e., the hot water supply machine is not operated, temperature is detected by a thermistor 10 at each specified time. By the detected temperature signal, a calculation memory means which is built in the control device 11 calculates a descending temperature in the specified time interval, and estimates the outside air temeprature by comparing relationship data between the descending temperature and the outside air temperature, which is previously stored, with the calculated descending temperature.