To provide a water heater capable of more surely preventing the freezing of water.

A first hot water supply temperature sensor 14 is disposed in a position near an outlet of a combustion chamber 3 at an upstream side of a hot water supply pipe 9, variations with time of a water temperature T1 detected by the first hot water supply temperature sensor 14 and a water temperature T3 detected by a water inlet temperature sensor 13 are monitored by a controller 20, a heater operation temperature and an off-temperature are increased when a state that the water temperature T1 is significantly lowered in comparison with the lowering of the water temperature T3 at a prescribed time is detected, and heaters 16, 16 are on/off-controlled at a water temperature higher than usual.

COPYRIGHT: (C)2011,JPO&INPIT