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Troubleshooting Aprilaire Humidifier



I have an Aprilaire 700M Home humidifier that was professionally installed and worked well last winter. This winter I replaced the pad and turned it on bit it's not working. The pad had no moisture at all so i figured it was not getting any water. So I attempted the following troubleshooting.

The water flowed fine to the solenoid and the screen was not clogged. The orifice and hose leading to the evaporator pad were not clogged either. When I turned the humidistat up I heard a click, but no sound at all from the solenoid valve. I tested the voltage in the wires coming from the humidistat and it read 28. So I took those wires and attached the directly to the solenoid wires. Again there was no click from the solenoid when I turned up the humidistat. So I ordered and installed a new 24v solenoid valve (#4040).

But here is the problem - I have the same exact symptom with the new solenoid valve! I again connected the wires from the humidistat to the solenoid and hear nothing. There is 28v coming from the humidistat, but when I connect the wires to the solenoid and measure the voltage reads .1. I don not have a 24v transformer or Id try testing with that.

Does this give anyone a clue to what the problem might be?


I know nothing about humidifiers but it sounds like the voltage is dropping out at a switch or relay at the control.  Check for a voltage at the switch while running, if you find 24 volts, that's your defective part. How old is the unit? I see from the owners manual, it has a 5 year warranty, Manual.

I bypassed the humidistat with a jumper wire and the original solenoid worked fine. So I ordered and installed a new humidistat and all is working again. I even got to return the new solenoid valve for a refund!

Nice! Thanks for the update.


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