Water heating apparatus

Abstract

A water heating apparatus is provided. The water heating apparatus includes a pump and is configured to be able to set a hot-water circulation route to circulate hot water discharged from a heat exchanger to be re-entered into the heat exchanger by operation of the pump. When a state of a hot-water supply operation in which a burner drives combustion is changed to an end state, hot water in the heat exchanger is circulated in the hot-water circulation route to suppress deposition of scale.

What is claimed is: 
     
         1 . A water heating apparatus comprising:
 a burner;   a heat exchanger for performing heat recovery from a combustion gas generated by driving combustion of the burner;   a hot water flow path connected to the heat exchanger in a manner enabling entry of water into the heat exchanger and discharge of heated hot water; and   a pump,   wherein a hot-water circulation route is settable, the hot-water circulation route circulates hot water discharged from the heat exchanger to be re-entered into the heat exchanger by operation of the pump, and   when a state of a hot-water supply operation in which the burner drives combustion is changed to an end state, hot water in the heat exchanger is circulated in the hot-water circulation route to suppress deposition of scale.   
     
     
         2 . The water heating apparatus according to  claim 1 , comprising a control means storing a data which defines a pump operation start condition for operating the pump during execution of the hot-water supply operation, wherein
 when the pump operation start condition is satisfied during execution of the hot-water supply operation, operation of the pump is started by control of the control means.   
     
     
         3 . The water heating apparatus according to  claim 1 , wherein during execution of the hot-water supply operation, when an incoming-water flow rate of incoming water to the heat exchanger decreases from a state exceeding a predetermined flow rate to the predetermined flow rate, operation of the pump is started, wherein the predetermined flow rate is a value larger than a minimum operating flow rate of the burner. 
     
     
         4 . The water heating apparatus according to  claim 2 , wherein during execution of the hot-water supply operation, when an incoming-water flow rate of incoming water to the heat exchanger decreases from a state exceeding a predetermined flow rate to the predetermined flow rate, operation of the pump is started, wherein the predetermined flow rate is a value larger than a minimum operating flow rate of the burner. 
     
     
         5 . The water heating apparatus according to  claim 1 , wherein during execution of the hot-water supply operation, when an incoming-water flow rate of incoming water to the heat exchanger decreases and a decrease range or a decrease rate is equal to or greater than a predetermined value, operation of the pump is started. 
     
     
         6 . The water heating apparatus according to  claim 2 , wherein during execution of the hot-water supply operation, when an incoming-water flow rate of incoming water to the heat exchanger decreases and a decrease range or a decrease rate is equal to or greater than a predetermined value, operation of the pump is started. 
     
     
         7 . The water heating apparatus according to  claim 3 , wherein during execution of the hot-water supply operation, when an incoming-water flow rate of incoming water to the heat exchanger decreases and a decrease range or a decrease rate is equal to or greater than a predetermined value, operation of the pump is started. 
     
     
         8 . The water heating apparatus according to  claim 2 , wherein an operating speed of the pump is higher after the hot-water supply operation is ended than during execution of the hot-water supply operation. 
     
     
         9 . The water heating apparatus according to  claim 3 , wherein an operating speed of the pump is higher after the hot-water supply operation is ended than during execution of the hot-water supply operation. 
     
     
         10 . The water heating apparatus according to  claim 5 , wherein an operating speed of the pump is higher after the hot-water supply operation is ended than during execution of the hot-water supply operation. 
     
     
         11 . The water heating apparatus according to  claim 2 , wherein in a case where the hot-water supply operation continues without being ended although a predetermined first time has elapsed since operation of the pump is started, operation of the pump is stopped. 
     
     
         12 . The water heating apparatus according to  claim 3 , wherein in a case where the hot-water supply operation continues without being ended although a predetermined first time has elapsed since operation of the pump is started, operation of the pump is stopped. 
     
     
         13 . The water heating apparatus according to  claim 5 , wherein in a case where the hot-water supply operation continues without being ended although a predetermined first time has elapsed since operation of the pump is started, operation of the pump is stopped. 
     
     
         14 . The water heating apparatus according to  claim 8 , wherein in a case where the hot-water supply operation continues without being ended although a predetermined first time has elapsed since operation of the pump is started, operation of the pump is stopped. 
     
     
         15 . The water heating apparatus according to  claim 1 , comprising a fan capable of supplying air to the burner, wherein
 the fan operates even after driving combustion of the burner is stopped to cause air to act on the heat exchanger.   
     
     
         16 . The water heating apparatus according to  claim 2 , comprising a fan capable of supplying air to the burner, wherein
 the fan operates even after driving combustion of the burner is stopped to cause air to act on the heat exchanger.   
     
     
         17 . The water heating apparatus according to  claim 1 , wherein after operation of the pump is started, at the time when a temperature of hot water flowing out of the heat exchanger drops to a predetermined temperature or below, or at the time when a predetermined second time has elapsed since the hot-water supply operation is ended, operation of the pump is stopped. 
     
     
         18 . The water heating apparatus according to  claim 2 , wherein after operation of the pump is started, at the time when a temperature of hot water flowing out of the heat exchanger drops to a predetermined temperature or below, or at the time when a predetermined second time has elapsed since the hot-water supply operation is ended, operation of the pump is stopped. 
     
     
         19 . The water heating apparatus according to  claim 1 , comprising a flow rate sensor provided at a position in the hot water flow path avoiding the hot-water circulation route to serve as a detection means of an incoming-water flow rate of incoming water to the heat exchanger, wherein
 the flow rate sensor is used for determination of a minimum operating flow rate of the burner.   
     
     
         20 . The water heating apparatus according to  claim 2 , comprising a flow rate sensor provided at a position in the hot water flow path avoiding the hot-water circulation route to serve as a detection means of an incoming-water flow rate of incoming water to the heat exchanger, wherein
 the flow rate sensor is used for determination of a minimum operating flow rate of the burner.