After double checking all connections, I noticed the connector wiring that plugs into temperature sensor seemed loose where it is attached to the connector. One wire had broken inside connector, after repairing machine is back to normal operation.
Check the start push button contact area on control panel. It has a plastic carriage that acts as a spring when pushed. If the carriage is broken contact is not made. I have repaired a few of these. If you push the button and it does not spring back, most likely the culprit
Also check the hose connecting the pressure switch to tub for a pinhole. Also be sure to use HE detergent if you get it going. I keep a roll of hose on my truck and always replace if I get the f20 code. Has fixed many of them.