Diagnosis
The float switch in the bucket well is stuck in the "up" position. This is almost always due to gunk, mineral scale, or a misaligned bucket.
How to Fix It
1) Unplug the unit. 2) Remove the bucket. 3) Look into the empty bucket compartment. At the back or side, you'll see a small plastic float on a hinge or guide. 4) Manually move that float up and down a few times. Feel for grit. If it's sticky, clean it and the well with a mix of vinegar and water to dissolve scale. Let it dry. 5) Reinsert the bucket, making sure it slides all the way in until it clicks.
If That Didn't Work
The float switch itself might have failed. It's a simple mechanical switch. If cleaning and jiggling it doesn't make it move freely and click, the switch may need to be replaced.
Heads Up
Also check the bottom of the bucket itself. If it's warped or cracked, it might not be pushing the float down all the way when you put it back in.