PURPOSE: To enable to change-over to a direct hot water supply system and to use hot water shower with high efficiency and yet prevent mud from adhering to a bath heater by a structure wherein ball valves are provided in two or upper and lower communicating pipes, which connect the bath heater and a bathtub and yet water supply pipe is connected at least to the lower communicating pipe.

CONSTITUTION: A valve seat 30, on which a ball valve 38 disengageably seated itself, is provided in a lower communicating pipe 28 and a valve stopper 32 is provided at a bath heater side. Furthermore, a water supply pipe 36 is connected to a branched part 34 extended downward from the pipe 28. An upper communicating pipe 26 has a construction similar to the lower communicating pipe 28 and, in addition, branches a pipe body 52 to the bath heater side. By opening a tap, the ball valves 46 and 38 are raised by water pressure so as to seat themselves onto the valve seats 40 and 30 respectively in order to block the communication between a bath boiler and a bathtub, resulting in flowing water upward in the bath heater 10 and discharging through the pipe body 52 of the upper communicating pipe 26. At this time, if a burner is in the ignited state, the water turns to be hot water by contacting with a heat exchanger, resulting in enabling to supply hot water directly through the pipe body 52.