There are four reasons.Firstly,there isn’t water in the water tank;secondly,the water pipe has freezed or jamed;thirdly,the sewer has a phenomenon of anti slope;fourthly,control system was failing.And there are four methods to deal with these questions.Firstly,inject water again;secondly,dredge the pipes and replace the valve;thirdly,correct the layout of pipes.You can try to choose one water mixing valve,next adjust the valve to the mixing of hot and cold state,then blocked the outlet,finally,use the municipal water pressure of the air inside the tube reached the tank again and again;fourthly,repair or replace the controller.