Maytag F 20 error, tried everything, what else?

I have a Maytag 4000 series washer throwing an F20 error. after tons of research I have, replaced the water inlet valve. replaced the water pressure switch, checked the line to the switch. cleaned the reservoir that is attached to the pressure switch. Checked the water pump and impellor. still throws a f20 code. Where should I look next? I am wondering if it is a board issue. I can run a cycle but after 10 minutes f20 shows. It will let me cancel then rinse and spin. any direction is appreciated. I am at a loss.