Usually, it's a problem with the control board. By replacing the control board, you should be able to fix the problem. However, it might also be a problem with the hose, something might be stuck in the hose. There is even a web site dedicated to the F1 error :) Whirlpool F1 Error web site. There you can find detailed instructions on how to check and clean the hose or if needed, replace the control board and also where to buy a proper one.