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Thread: Nest (3rd Gen) thermostat gives error code E104

  1. #1
    Junior Member

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    Nest (3rd Gen) thermostat gives error code E104

    Hello

    I have a Lennox furnace, ECW NCM-300 control panel and two Nest (3rd Gen) thermostats in my home. The Nest thermostat in my first floor works great and has been perfect.

    My Nest thermostat on the 2nd floor gives an error code E104 (overcurrent detected in G/Fan wire). I've been trying to get this sorted out for a long time with NO solution in sight...




    Has anyone seen anything like this before? Can experts here chime in?

    Thank you
    Max

  2. #2
    Administrator

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    Have you look into wiring in a isolation relay like the one in the like below that the Nest G terminal would control?



  3. #3
    Junior Member

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    Quote Originally Posted by Thermostat View Post
    Have you look into wiring in a isolation relay like the one in the like below that the Nest G terminal would control?
    Could you please explain? I'm handy but short on knowledge/experience with these Nest thermostats...

    This is the 3rd time I installed these Nest's but the only time I started having a lot of trouble. If you're talking about the "PAM-1" relay (popped up multiple times in my search on this forum), I'd love to know more about the wiring part of this process...

    Thanks a lot for your time!

  4. #4
    Administrator

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    See attached drawing. Wiring only shown for the isolation relay. You could use any normally open relay that has a 24vac coil but the Senva or the pam relay would be easier to install.

    Click image for larger version. 

Name:	ECW Nest.jpg 
Views:	284 
Size:	43.3 KB 
ID:	1605




  5. #5
    Junior Member

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    Quote Originally Posted by Thermostat View Post
    See attached drawing. Wiring only shown for the isolation relay. You could use any normally open relay that has a 24vac coil but the Senva or the pam relay would be easier to install.

    Click image for larger version. 

Name:	ECW Nest.jpg 
Views:	284 
Size:	43.3 KB 
ID:	1605



    Great, thanks a lot for the illustration above.. Will try it.

    Question: So what should the Nest thermostat's C-wire go to now? Or is it NOT necessary anymore because the power is drawn from the control-board/furnace?

  6. #6
    Administrator

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    All of the other wires that connect from the Nest to the ECW will stay as there were. Only the G wire changes. The C terminal on the ECW will now have 2 wires.

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