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F-21 mean long drain, you need to clean your drain pump trap, this is what the drain pump looks like its sideways in the picture however, remove the screws # XXXXX on this diagram and take the access panel off, the pump will be right there, unscrew the cap counterclockwise and pull the trap out, get some towels ready there will be water. clean the trap and put it back in, this should take care of the issue, if not your pump is bad or one of the drain hoses itself is clogged, here are the steps in the manual,
1. Check the drain hose and make sure it is not plugged or
2. Unplug washer or disconnect power.
3. Check the electrical connections at the pump and make sure
the pump is running.
4. Check the drain pump filter for foreign objects.
5. Plug in washer or reconnect power.
6. If the above does not correct the problem, go to step 7.
7. Unplug washer or disconnect power.
8. Replace the pump.