The F21 code on many Kenmore Elite front load washers indicates a long drain problem. This can be caused by excessive suds or a restriction in the drain system.
Check the tub for excessive suds. If you see this condition, then I recommend that you drastically cut back on the amount of HE (High Efficiency) detergent that you are using in the washer. You should only need about 1 tablespoon of detergent per load. Once the foam dissipates, you should be able to run a drain/spin cycle on the washer.
If you see no excessive suds, then you could have a clog or restriction in the drain system as noted above. Check the washer drain. Check the drain hose for kinks or clogs.
The image below shows how to access the drain pump clean-out filter on most Kenmore Elite front load washers. If the water is already drained out of the washer, you can
unplug the washer
and pull off the bottom front service panel. Arrange a shallow pan or towels to catch residual water that will drain out of the washer when you remove the filter. Remove the clean-out filter and check this area for lint or foreign objects.
If the washer is full of water and the door is still locked, you can manually unlock the door by
unplugging the washer
and removing the bottom front service panel. Carefully reach up along the inside of the front panel and pull down on the manual release tab that is on the bottom of the door lock assembly until it clicks. You can then open the washer door and drain the water using a wet/dry shop vacuum.
These tips should help you resolve a drain problem in your washer. If you have a different problem or need more assistance, reply with additional details and the full model number of your Kenmore Elite washer.