You may have already figured out the problem, but this happens when the valve on the right side (1/2 way up the side wall) is covered with a large dish. It will cause the water to leak all over the floor and the pump runs continously.
If this is not your problem, the other cause is the drain tube underneath which must be a certain height. If it is not and is hanging down because of the way the unit is installed, a similar thing can happen.
B
June 2007