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

The F21 error code signals a drain problem with the washer. Press PAUSE/CANCEL twice to cancel the cycle and unplug the washer, 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 your cycle, and press START; if the issue persists, call for service. (Page 23)