What does the F21 error code mean and how do I fix it?

The F21 error code indicates a drain problem. Select PAUSE/CANCEL twice to cancel the cycle, then unplug the washer and check whether the drain hose is kinked, frozen, clogged, or positioned more than 96 inches (2.4 m) above the floor. Reconnect power, re-select the cycle, and press START; if the problem continues, call for service.