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

The F21 code indicates a drain problem. Select PAUSE/CANCEL twice to cancel the cycle, then 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 persists, call for service.