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Thread: Nest ain't heating with 24V R and W two-wire system...

  1. #1
    Junior Member

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    Unhappy Nest ain't heating with 24V R and W two-wire system...

    My house has a Williams Forsaire Counterflow wall heater. It is controlled by a Honeywell S8600B pilot/ignition. The current thermostat is a White-Rodgers 1F56W-444 mercury unit. By all accounts, the current thermostat and the Honeywell are 24V systems, though the only wiring the thermostat has is a red R wire and a white W wire coming out of the wall.

    When I go through the motions with my Nest E, it powers up (so the R wire should be good), and it "detects" a W wire during setup, so I assume that's good...but it just won't get the heater to spool up. When I jump the W wire to the R wire, everything behaves as it should:

    1) Pilot sparks up the gas for a few seconds.
    2) Fan kicks on and blows the heat out.

    When the wires are disconnected:

    1) Heat turns off.
    2) Fan spins until residual heat is blown out.

    All the Nest needs to do is jumper these two wires internally, but it ain't doin' it. I'm boggled. It really seems like I just have a loose connection or something, but I've jiggled, tugged, crammed, and wiggled...What are the chances my Nest is just busted, either due to defect or me mucking around with it hanging off the wall?

  2. #2

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    Not using a common wire may be your issue. Is there an extra wire that you can use for a common wire on the Nest. On a system like yours I would recommend having a common wire even if it is not related to the issue that you are having now.

  3. #3
    Junior Member

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    Yeah, that appears to be it:

    There's one battery-power wifi Thermostat, but even they say a common wire is a very good idea. I don't want to be changing batteries in my thermostat every month...

    I guess the question is now, how much do I trust my fishing skills? Am I willing to crawl under my house?

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