Question about Aprilaire 700 Humidifier

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Water not getting to panel when furnace is on

I detected that while my furnace was running, there was no water delivery to the humidifier water panel - that is, the solenoid valve had not triggered. When I moved the humidistat dial to "test/reset", the solenoid activated and water began to flow and continued to flow during the heating cycle. The dial setting was returned to its normal position (35%) during this time as well. During the next heating cycle, however, the same scenario ensued - no water delivery to the panel. I sought some professional advice and was told that there was a high probability that the solenoid was either defective or clogged in some way. I replaced the solenoid valve with a new one (the old one was not clogged in any way and inlet and outlet tubes were both clean as well) and am still having the same issue. Evidently, the problem is not the solenoid but something else. I'm thinking perhaps that the humidistat panel itself may be defective in some way. Any ideas?

Posted by Dan Jacobson on

  • 5 more comments 
  • Anonymous Dec 07, 2007

    i changed the filter at the begining of the water goes to panel , when heat comes on , tried to to do test,no cliking sound from the seliniod.blew air on the humidstat

  • Hawk22 Dec 07, 2007

    A couple of issues. First, the unit doesn't seek to turn on unless I set the panel to the Test position. Once i do this, the water starts to flow, but never makes it thru the solenoid. I've cleaned and even removed the in-line strainer, but the water still never gets thru to the outlet hose.

  • scubascout Dec 11, 2007

    I have a similar yet different issue. Sometimes there is no water going through the system (nothing coming out to the drain) which is accompanied (sometimes but not always) by a vibration in the pipe from the water heater to the unit. Any ideas what could be causing this?

  • bsn33m Dec 14, 2007

    My Aprilaire 760 doesn't turn on. The solenoid clicks and water begins to flow, but just a fraction of a second that, the solenoid clicks off. I just finished replacing the solenoid and...same problem. The solution lies somewhere else - but where?

  • Anonymous Dec 18, 2007

    brand new unit.

    installed in manual mode

    operates only in test mode.

    will not turn on solenoid when turning dial off and then slowly back on

    does not come on when blower operates and furnace operating.

  • Anonymous Dec 23, 2007


  • GP09 Jan 11, 2009

    I am not getting any water through the solenoid valve, even after I have taken it apart and cleaned it. It seems like there is no power to the unit at all. 



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I had a problem quite similar to this. It was the power connector. This is the 4-pin white connector that engages when the cover is removed/replaced when accessing the water panel.

One of the pins was loose in the connector thereby supplying intermittent 24 volt power for the solenoid that is powered by the fan motor control board transformer in the humidifier cover next to the fan motor (not seen unless fan is dissembled).

If you are technical such as I am this is easy to fix by removing the connector, removing the loose pin, and often each retaining clip on the connector pin can be bent out slightly, then replace the pin, and then it should be fine. Also, it's best to check this out on a bench while running the entire unit. You also might need to replace the entire power connector. Sometimes it's easy to think the problem is a defective solenoid or fan motor/transformer board, etc. It's frustrating, because sometimes the humidifier works perfectly, and then sometimes there is no water flow. Since I did this mine has been 100% OK.


Posted on Feb 07, 2008



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Assuming that your humidistat panel in on the cold air return, I would remove the panel and check that some lint or dust possibly is stuck to the sensor. Also check the operation of the solenoid easily when the furnace is running by turning the dial back and forth and you can hear the solenoid open and close.

Posted on Mar 07, 2007



The humidistat detected that the RH in the area of the sensor was as required or exceeded the setting as an upper limit

Posted on Mar 06, 2007

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