Sounds like the pressure switch or solenoid is faulty. This is a valve or electrically operated tap/cock that is in the water supply line. connected to a hose that goes to bottom or side of drum. At least that is what is like on hotpoints. If you have hot and cold fill you will have two solenoids . Actually from memory this function is carried out by a diaphram unit that registers pressure via the hose, then sends signal to water supply solenoid to stop water supply. if you disconnect hose and blow into pipe on diaphram unit, you should hear the solenoid activating. hope this is some help.
Phil.
June 2009