CONTROL METHOD FOR ADDING WATER TO BATH

PURPOSE: To keep a drop of water temperature in a bathtub effected by one water- adding operation approximately constant regardless of seasons by providing a water temperature meter for detecting water temperature of water added to the bathtub and controlling the amount of the additional water in such a manner that the amount of the additional water is increased as the detected water temperature becomes higher. CONSTITUTION: A water circuit 3 for supplying hot water from a heat exchanger 10 provided in a bath heater 1 to a bathtub 2 is provided with an open/close valve 4 and a water level sensor 41 for detecting water level in the bathtub and the water circuit 3 in an upstream side of the bath heater 1 is provided with a water temperature meter 5. An additional water amount measuring device 74 for measuring the amount of city water supplied to the heat exchanger 10 is provided in a further upstream side. When a water addition switch 25 is turned on, the open/close valve 4 is opened by a control device 7 and temperature detected by the water temperature meter 5 is written on a water temperature memory and a variable is set to a specified value. If the detected temperature is lower than a value read out from a table corresponding to the variable, an amount of additional water which corresponds to the temperature is selected and the additional water is supplied to the bathtub.