I recently had this problem. The machine would fill with water when not switched on. It started happening after having a new kitchen fitted. The water was getting into the machine from the outlet pipe after using the sink.
A friend remembered that the outlet pipe must be higher than the connection to the sink's U-bend. Check that the outlet pipe is hooked up and then angled downwards to the connection of the sink’s U-bend.
It solved my problems and we no longer have flooding.
PS Check for blockages at the connection of the outlet pipe and the U-bend.
John
July 2006