What does the F21 error code mean on my Whirlpool washer?

The F21 error code indicates that drain times are longer than expected. This is typically caused by a kinked or clogged drain hose, or by using non-HE detergent which can create excessive suds and drainage issues. Check your drain hose for kinks or blockages, and ensure you are using only HE High-Efficiency detergent.