Water heater

A water heater comprising:

• a plurality of stages of burners;
• a water supply pipe;
• a hot water outlet pipe;
• a heat exchanger coupled to the water supply pipe and the hot water outlet pipe, the heat exchanger being heated with the burner;
• a passing water quantity control unit disposed in the water supply pipe, the passing water quantity control unit controlling a passing water quantity in the heat exchanger;
• a temperature detection unit that detects a hot water temperature inside the hot water outlet pipe;
• and
• an operation control unit that executes an output hot water temperature control in which a detected temperature obtained from the temperature detection unit is caused to match a set temperature by a switching control of combustion stages of the burners and an operational control of the passing water quantity control unit, wherein
• the operation control unit, upon confirmation that a predetermined start condition of a passing water restriction is satisfied at a start of a hot water supply, performs the output hot water temperature control by calculating a target flow rate that is smaller than a predetermined water quantity and causes one of no switching or a minimum count of switching of the combustion stages of the burners and, by configuring the passing water quantity control unit to have the target flow rate, and upon confirmation that a predetermined release condition of the passing water restriction is satisfied, executes the passing water control in which the passing water quantity is returned back to the predetermined water quantity by gradually releasing the passing water restriction.