Model 440 not shutting off

Mar 13, 2009

-   I have a similar problem on an Aprilaire 550. I have not solved my problem but can help you identify the source. On my unit a humidistat, the solenoid valve, a 24 volt transforer and a current relay are wired in series. In theory, when the thermostat calls for heat, the furnace exhaust fan cuts on, the burners then cut on, then the fan cuts on. If the humidistat calls for humidity, the water valve solenoid cuts on when the fan starts, assuming that the relay senses current going to the fan. When the temperature is reached, the furnace and exhaust fan cuts off. However, the fan continues to run for a time until the heat exchange box cools down. The fan then cuts off as does the humidifier since there is no current flowing through the wire to the fan.

Potential solutions:

1. You didn't wait until the fan cut off to see if the humidifier shut down.

2. Since you replaced the solenoid, the problem must be in the current relay sensor. Move it around and see if the humidifier cuts off. If it does, the relay was picking up current from another source or was stuck. If it doesn't cut off, it is probably bad.

I did all of this and put in a new current sensor but it did not solve the problem. I believe the new part is bad but am not sure.

Let me know what you ultimately found. -   Guest

Mar 08, 2009

-   I have the same problem with the unit. It will not shut off after the furnace stops running. I replaced the solenoid and that didn't help.
Can you answer on this one? Would I need to replace the humidistat?-   Guest

Nov 25, 2008

-   I had the same thing happen to me today. I installed a new solenoid valve and now the water does not stop running when the furnace shuts down.-   Help welcome