If its an older unit or it got heavy use it could be the motor they tend to sputter as there going out, as it rotates the electricity hits a burnt spot inside the motor and shuts itself off can you turn it on manually? they usually put a swithc on the tank itself if the problem doesnt occur when you switch it then it could be the hose itself normally they control the off/on use a meter to check the continuity beteen the two copper plates that are on the end of the hose ( the wall end )