Diagnosis
The control board isn't getting the signal to run, usually due to a faulty wall humidistat, a miswired control, or a blown low-voltage fuse on the board.
How to Fix It
Bypass the wall humidistat to test it.
- Turn off power.
- At the unit's control board, find the two low-voltage wires (typically labeled 1 and 2) from the humidistat.
- Disconnect them and temporarily twist the two board terminals together with a wire nut.
- Restore power. If the unit runs, the wall humidistat is faulty and needs replacement.
If That Didn't Work
Check the 3A or 5A automotive-style fuse on the control board. If it's blown, replace it with an identical fuse. If it blows again, there's a short circuit needing a pro.
Heads Up
When bypassing the humidistat, the unit will run continuously. Don't leave it like this permanently—it's a diagnostic step only. Reconnect the proper control once diagnosed.