This is too late to be of use to the original poster but might help others ....
A while ago I had an f04 error on Bosch Exxcel washing machine. Checking t'internet on the old tom tutor I found that the error is likey to be either a blockage in the filter, a blocked drainage pipe, the little blockage detector pipe getting block or the drainage pump not working properly.
I look in the filter - nothing and I could see the propellor in the pump turning ok. I took the lid and the front cover off and checked the grey drain pipes by unhooking the drainage pipes and the sticking a curtain wire down them and blowing down them aswell. The little blockage detector pipe is only about 2foot long and very thin and runs up from an opaque plastic tube connected to the sump (below the drum) to a plastic oval shaped part that houses a pressure detector - disconnected it at the top and blew into it- seemed ok. Then had a look at the pump at the back of the filter. I could see a bit of soot on the pump case. I dismantled the pump and the back of the magnet coil were the single strand wire connects the 2 coils was black so I suppose it was slowly failing.
I'm no washing machine engineer and not very technically minded but this wasn't difficult to fix.
First off - Look up your model on the Bosch customer services website and look for spare parts and you should find a parts diagram - you'll need to do this to get the part no to order from them - pump cost me just under £60 and also if like me you've never opened the machine before then its a good reference guide.
Tools needed - star screwdriver or drill (dont know the technical term but NOT a philips though you need one of them too) needed to open it up; pliers (long nose are better) for opening clips; Bucket, towel and a baking tray for catching water.
Top tip - When your struggling to get the retaining ring back onto the big rubber drum seal - cross your arms.
Never looked but you tube might have some videos. I think Bosch site had a very basic video.
Got dad skills
September 2009