Water heaters and flow control method

Providing inhibit scale adhering to the inner wall of the liquid flow passage is heated in the heat exchanger constituted of the heater, the heat exchange performance due to reduced inhibition of scale is deposited and the flow path caused by clogging of the heater. In the tank by the upper (1) and the heat exchanger (3) circulates the heated liquid is applied pulsating flow, release the inner wall (heat transfer surface) is heated in a heat exchanger the liquid flow passage (31) in (3) the precipitated scale, and the number of the heat exchanger between the water tank and circulating the heated liquid circulation control in three or less. The flow rate of the flow control unit (101) so that the heat exchanger (3) of the heated liquid flow path (31) by heating the liquid pulsation, and the control flow path is heated in the liquid (31) through which heated liquid, such that cycles is three or less, the number of cycles based on stored in the water tank total capacity (1) of the heated liquid, the tank is the total capacity of the heating liquid reaches a predetermined temperature of the boiling time and the liquid flow path is heated in the (1) (31) the heated liquid flow is determined by, and represents the total capacity of the tank is stored in a heated liquid (1) by the number of times in the heat exchanger (3).