Bosh WFF2001 water coming back into the drum?

It depends on your installation. The two main ways are to hook the waste outlet into a drainage downpipe fitted for the purpose. It should be about 1 metre high.
The other way is to connect the outlet hose to the sink wastepipe using an adaptor. The adaptor should have a non-return valve fitted within it.

If it was okay before and is playing up now, the machine could have a blockage in the waste pipe so it can't pump all the water out which will return when the machine stops spinning.

Colin
January 2008