WFW9550WR00 Whirlpool duet steam washer I just cleaned out the filter (found a bunch of coins). Tried to start a load and got F21 error again. Any tips?

The coins you found in the filter damaged the impeller on the pump which is why you are still getting the error. It can't drain fast enough with the damaged impeller to satisfy the control. You will need to replace the drain pump. The drain pump for that model is listed below:

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