The drain hose has a non return valve so you cannot blow back water anyway just give yourself a hernia fred. you havnt given proper model no it is engraved on top edge of stainless steel door so i will guess your model and say that you probably have a blockage in the pump which is accessible from inside the dishwasher, remove filter and look down in sump you should see white plastic pump cover on left held in with 1 torx 20 screw. Undo screw and note which hole it came out of (2 holes 1 screw) lift cover and check impellor and under it. Other possibilities grease blockage at sink connection. Cheers
Kenjo, June 2012
