Diagnosis
The float sensor inside the water reservoir is stuck or gunked up, so the machine thinks it's empty even when it's not.
How to Fix It
Unplug the unit and empty the reservoir. Tilt it forward over a sink to drain any hidden water. Manually move the small white plastic float up and down a few times to free it. Clean any visible mineral deposits off the float and its chamber with a soft cloth and a bit of white vinegar.
If That Didn't Work
The sensor itself might have failed. The only real fix for that is contacting Northair customer support for a replacement part or repair.
Heads Up
This is almost always a cleaning issue. Using filtered water and running a vinegar cleaning cycle every few weeks prevents it.