The humidistat was replaced. The wiring looks the same as it did before. However, the solenoid only opened when the blower was on. Now we hear the solenoid opening at all times of the night whether the blower is on or not. The tech did say it was going to run a lot for a few days because our humidity was so low. We have the dial on 5 and it clicks at about 4.5 but never has reached 5. It was 44 hours ago the humidistat was swapped out. Is this normal?

Update: The tech who installed the humidistat said the furnace installers (several years ago) had added a transformer for the humidistat which bypasses the blower. Please see picture. enter image description here

1 Answer 1


No, it is not normal. The solenoid allows water to run over the humidifier's screen. If the blower isn't running....it's a pointless waste to have water running.

I assume you aren't confusing the running of a condensate pump (if you have one) with the solenoid. The pump can kick on even if the blower isn't running.

  • I agree and it can be really bad depending on the type of unit it should never run without the blower. Good call on the possibility of a condensate pump.
    – Ed Beal
    Dec 30, 2020 at 17:52

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