Diagnosis
The condensate pump has either lost its prime (got an air lock) or the inlet screen is clogged with gunk from the internal tank.
How to Fix It
Unplug the unit. Pull out the internal bucket. Locate the small rubber pump inlet inside the bucket compartment—it's a little nozzle or grate. Clean any visible sludge or mold off it with a brush and vinegar. Then, pour a cup of water directly into the pump's reservoir (the area where the bucket sits) to re-prime it. Plug it back in.
If That Didn't Work
Check the drain hose for a severe kink or an upward slope. The pump is weak; the hose must run downhill from the unit all the way to the drain. Straighten the hose path.
Heads Up
Never let water sit in the internal bucket for priming. Always use fresh water to avoid pumping debris into the pump mechanism.