May duet washer is showing an error code F20

Here are some manuals to help you: https://dl.dropbox.com/u/8010163/Und...c%20washer.pdf
https://dl.dropbox.com/u/8010163/Whi...0Job%20Aid.pdf
Whirlpool Duet Washer Repair Manual Diagnostic Tests
The problem is that the water level switch hose is clogged. Remove top and you will see a 4" round switch with two wires attached operated by the diaphragm inside; it has a clear plastic hose going to it to operate the water level switch by pressure. It's clogged up. Remove it from switch and blow through it to unclog it. Replace and you are done. (See: Duet GHW9150P Front Load Washer: error code f20? - FixYa )