My Bosche shu5315uc dishwasher works fine in every way except for the problem listed below. It started happening all of a sudden.

Water continues to come from the base even when dishwasher is off. It is a slow trickle but fast enough that I hear a hissing sound and it fills up the dishwasher. It stops if I shut off the main water vale under the sink.

Any ideas how to fix this problem? Thanks for your help.