F20 is a communication error between the display control board and the relay control board. Pull the oven forward and remove the back panel. Check the wire connections between the display board and the relay board. If the connections check good, replace the display control board
one of 2 things...depending on the version you the unit you have.
1.
F0 & F1
EOC (Electronic Oven Control) failure
Replace
2.
F1
Circuit board defective
Replace control board
you can go here for parts and videos on it's DIY fix.
repairclinic.com
or appliancepartspros.com
have the model# handy,