Whirlpool Duet F20 which part to order first?

[mcanterbury]

I’ve been getting the F20 error when my washer begins to load. I’ve been down the whole list of whirlpool recommendations of what to check (blew in flowmeter, blew in pressure valve hose, verified pressure hose is fine, cleaned out filter under drum, ran CCU test & still got F20 error, water hoses are all fine, water pressue is good). At this point I feel I need a part but not still not sure which one. What part would you start with replacing first? flowmeter, inlet valve, pressure switch? any advice would be appreciated.