There are five reasons.Firstly,municipal water is too low or cut off the water supply;secondly,the water pipe has freezed or ruptured;thirdly,the vacuum tube was damaged;fourthly,the water tank is leaking;fifthly,control instrument is failed or electromagnetic valve was broken down.Of course,there are five methods to deal with them.Firstly,feed water in the water trough;secondly,you should dredge pipe and do some heat preservation measures;thirdly,renewing the vacuum tube;fourthly,refer to the treatment of heat presrevation water tank’s leakage;fifthly,repair or change the spare parts.