Diagnosis
The drain hose isn't seated correctly or has an air lock. The unit's internal pump (if equipped) or gravity drain needs a clear, downward-sloping path.
How to Fix It
First, ensure you've pushed the drain hose firmly onto the barbed outlet at the back of the unit—it needs a solid 'click' feel. Second, and most critical, the hose must have a consistent downward slope from the unit to the drain. Any loops or rises will create an air lock that prevents flow. Straighten the hose.
If That Didn't Work
Check for a small rubber stopper or plug still inserted in the drain outlet. It's easy to miss. Remove it from the outlet or from inside the hose.
Heads Up
The internal bucket must be in place for the drain to work. The float switch mechanism is still active. If the hose is kinked or blocked, the unit will fill the bucket as a backup, then shut off on red light. Always use a standard 5/8" ID hose, not a garden hose.