Error code E4 means the bottom sump has too much water in it. The polystyrene float floats up and trips a microswitch (at the front of the machine).
The black plastic covers facing front can be removed (quite frim) and the sump mopped out with a sponge - this should release the float switch.
General concensus of opinion is this is a poor design fault - so you may need to do this at intervals. I've had to do this about 4 times now - machine is about 2 years old. (I also got a small file to the lugs on the covers to make subsequent removal easier).
If there is none or very little water in the sump, I suppose it's possible the float switch has tripped, and then lodged in the "up" position.
On my BDW45.1 the float had actually stuck down to the metal base (soapy water - cheap tablets i guess), and the motor got flooded causing the house fuse board to trip. Cost me a new motor (and I can tell you where to get one much cheaper than mainstream suppliers if you need one). I have attempted to cure this by stopping the float from completely resting flat (I glued a strip cut-off a cable tie-wrap to the metal base - should stop the two faces coming together).
I don't know why water collects in the sump - here's my guesses:-
1. there are two small drain hoses into the sump, one comes from the turret shaped overflow in the bottom of the cabinet designed to prevent the machine overfilling. But if there isn't a well-designed valve in it I guess water could be ricocheted into it from the wash jets hitting the dishes..
2. there are vents in the sides of the cabinet to let steam escape - I suspect if water was getting out through these there would be evidence on the inside of the side panels - which there isn't.
Hope this info helps
daba
October 2008