You could have a stuck solenoid valve. Try this: Set the water temp on cold. Turn on only the hot water. Does hot water try and fill the drum? If so then there is a problem with the hot solenoid.
Next set the water on hot. Turn on only the cold water. Does cold water try and fill the drum? If so then there is a problem with the cold solenoid.
Next set the water on hot. Turn on only the cold water. Does cold water try and fill the drum? If so then there is a problem with the cold solenoid.