| 摘要 |
<p>PURPOSE:To ensure an accurate failure diagnosis by detecting a pressure difference between upstream and downstream sides of a water amount control valve, setting failure diagnosis conditions based upon the pressure difference, and diagnosing the failure of the water amount control valve based upon a motor control signal. CONSTITUTION:There are disposed a flow sensor 30, an input water temperature sensor 40, an output hot water temperature sensor 60, and a water pressure sensor 65. Detection signals are inputted into a control unit 70. A water amount flowing in a water distribution pipe 20 is set on the basis of the set temperature, the input water temperature, and maximum combustion capability, and PI operation is conducted on the basis of a deviation between the detected amount of water and the set amount of water to determine a duty ratio. An opening of a water amount control valve 50 is controlled through a motor 56 in conformity with the resulting duty ratio to control the amount of water and hence the output hot water temperature. Upon a failure diagnosis of the water amount control valve 50 a failure is decided if the duty ratio exceeds a set threshold and continues set time. The set threshold and the set time used for the decision are set on the basis of a pressure difference between the upstream and downstream sides of the water amount control valve.</p> |
