Diagnosis
Error F21 is a "Long Drain" error. The washer is taking too long to drain the water, exceeding its programmed time limit.
How to Fix It
Address the three common causes of slow drainage. 1. Clean the drain pump filter as described in . This is the primary fix for F21. 2. Check that the drain hose is not kinked, pinched, or clogged. The hose should have a high loop. 3. Verify the household drain line (standpipe or utility sink) is not partially clogged or undersized, causing slow outflow.
If That Didn't Work
The pressure switch (water level sensor) may be faulty and not detecting that the water has drained, or the drain pump may be weak. These require component testing with a multimeter.
Heads Up
Repeated F21 errors can cause the washer to stop a cycle prematurely. It will not proceed to the spin cycle, leaving clothes very wet. Consistently cleaning the drain pump filter every 3-6 months prevents most F21 occurrences.