PURPOSE: To obtain the title heater which sounds an alarm when a joint of a hot-water piping comes off.

CONSTITUTION: A radiator 1 for indoor installation and a hot water supply device 2 for outdoor, and a receptacle 3 for an inside wall are provided. One ends of reciprocating pipes 4, 5 for feeding hot water are linked to the radiator 1, while the other ends thereof are integrated with plugs 8, 9 having normally close valve. Hot-water reciprocating pipes 6, 7 linked to the hot water supply device 2 are connected through the wall to receptacles 12, 13 provided in the receptacle 3. The plugs 8,9 have contact pieces 10, 11, and the receptacle has a short circuit piece 14 to make a receptacle switch, which is connected to a control circuit of the radiator 1.