W640 - Water Outlet Fault
I solved this problem this morning, after several months with intermittent "water outlet fault" error messages.
Our pin trap was cleared many times over the months. The propellor turned freely. However, the problem persisted.
So I unplugged the machine, removed the back panel (8 or so hex screws) and located the point where the drainage hose meets the water draining pump. I then separated the hose from the pump and found 2 United States 10-cent pieces lodged together with gunk that effectively blocked the drainage hose. 10-cent pieces ("dimes") are the perfect diameter to get stuck there and not appear in the pin trap where you could easily see and remove them.
Three loads later, the machine is working according to spec. Hope this helps.