Water heater and control method therefor

1. A water heater comprising:

one or a plurality of heat exchangers that heat tap water or return water with combustion heat generated by combustion of a burner, the return water being from a hot water supply part;

a circulation line that supplies the tap water or the return water, which is heated by the heat exchangers, to the hot water supply part, and circulates the return water from the hot water supply part through the heat exchangers;

an incoming water pipe that joins the circulation line between the hot water supply part and the heat exchangers, and supplies the tap water to the circulation line;

a circulation pump that circulates the return water through the circulation line; and

a control unit that links the combustion of the burner to operation of the circulation pump, calculates a flow rate for supplying the hot water required for a thermal process after a predetermined time has passed since hot water supply had been ended by shut-off of an opening and shutting faucet that is set on the circulation line, starts the operation of the circulation pump and the combustion of the burner, the combustion corresponding to a quantity of heat for making the return water, which flows at the flow rate, a predetermined temperature, and stops the operation of the circulation pump and the combustion of the burner when a predetermined time of the thermal process has passed.

2. The water heater of claim 1 , further comprising:

a temperature sensor that detects temperature of the tap water and/or the return water at an inlet part of the heat exchangers; and

a flow rate sensor that detects flow rates of the tap water and/or the return water for the heat exchangers in the circulation line,

wherein the control unit calculates required quantity of heat based on an incoming flow rate for the heat exchangers and temperature detected by the temperature sensor, stops combustion of the heat exchangers based on the required quantity of heat, and stops the circulation pump.

3. The water heater of claim 1 , wherein the control unit further causes the circulation pump to operate when the flow rate in the circulation line is a predetermined value or over or when the required quantity of heat of the tap water and/or the return water is a predetermined value or over, during the stop of the circulation pump.

4. The water heater of claim 1 ,

wherein the circulation line includes

a hot water supply pipe that supplies hot water from the heat exchangers to the hot water supply part;

a return pipe that returns the return water from the hot water supply part to the heat exchangers; and

a branch that joins the incoming water pipe to the return pipe, and makes the tap water join the return pipe, and

wherein the circulation pump is disposed on the return pipe.

5. The water heater of claim 4 , wherein a check valve that prevents a back flow of the tap water or the return water is provided on the incoming water pipe and the return pipe.

6. The water heater of claim 1 , wherein the control unit causes the circulation pump to move to freezing prevention operation when hot water temperature in the circulation line is predetermined value or below.

7. The water heater of claim 6 , wherein the control unit includes a control switch for controlling operation for the circulation pump, and causes the circulation pump to execute the freezing prevention operation according to setting of the control switch.

8. A water heating control method, comprising:

heating tap water or return water by one or a plurality of heat exchangers with combustion heat generated by combustion of a burner, the return water being from a hot water supply part;

supplying the tap water or the return water, which is heated by the heat exchangers, to the hot water supply part, and circulating the return water from the hot water supply part through the heat exchangers via a circulation line by a circulation pump;

supplying the tap water to the circulation line by joining the tap water to the circulation line between the hot water supply part and the heat exchangers; and

linking the combustion of the burner to operation of the circulation pump, calculating a flow rate for supplying the hot water required for a thermal process after a predetermined time has passed since hot water supply had been ended by shut-off of an opening and shutting faucet that is set on the circulation line, starting the operation of the circulation pump and the combustion of the burner, the combustion corresponding to a quantity of heat for making the return water, which flows at the flow rate, a predetermined temperature, and stopping the operation of the circulation pump and the combustion of the burner when a predetermined time of the thermal process has passed.

9. The water heating control method of claim 8 , further comprising:

detecting temperature of the tap water and/or the return water at an inlet part of the heat exchangers;

detecting flow rates of the tap water and/or the return water for the heat exchangers in the circulation line; and

calculating required quantity of heat based on an incoming flow rate for the heat exchangers and the detected temperature, stopping combustion of the heat exchangers based on the required quantity of heat, and stopping the circulation pump.

10. The water heating control method of claim 8 , further comprising operating the circulation pump when the flow rate in the circulation line is a predetermined value or over or when the required quantity of heat of the tap water and/or the return water is a predetermined value or over, during the stop of the circulation pump.

11. The water heating control method of claim 8 , further comprising moving the circulation pump to freezing prevention operation when hot water temperature in the circulation line is a predetermined value or below.