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How to wire relay so wifi stat can control millivolt gas valve??

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Motorapido
Motorapido Member Posts: 307
Dummy me lost his wiring notes from last year. I installed a wifi thermostat in parallel with a millivolt stat to control a standing pilot gas heater with a millivolt gas valve. This allowed me remote temperature monitoring and adjustment, with the millivolt stat still in the circuit to call for heat during power failures.

It worked great, but when construction workers were doing demolition for my remodel, they disconnected the stat and the fan center relay before I had a chance to write down the wiring info. Can anybody advise me on how I connect the wifi stat to the relay?

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  • ratio
    ratio Member Posts: 3,696
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    You don't have enough pics to tell, but the first thing I'd try is swapping the red & green wires. Red is usually the power to the thermostat, white is usually the heat call back to the furnace, & green is usually the fan call—unless you don't need a fan call & do need a common, then it's usually the common.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,839
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    R, C & W on the thermostat. R goes to R on the fan center. C goes to C on the fan center and w has to pull the relay coil in along with a C wire,

    Supposed to use a relay with special contacts to switch the millivolt but I have used regular relays with no issue. need pics of the relay to be more specific.
  • Motorapido
    Motorapido Member Posts: 307
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    R, C & W on the thermostat. R goes to R on the fan center. C goes to C on the fan center and w has to pull the relay coil in along with a C wire,

    Supposed to use a relay with special contacts to switch the millivolt but I have used regular relays with no issue. need pics of the relay to be more specific.

    Thanks. So the W wire from the stat -- which lug does it connect to on the relay? This fan center relay has a bunch of wires that come off the back of the assembly. I was advised on a separate forum not to use any of those wires and to tape the ends and bundle them, unused, inside the junction box that the fan center mounts onto.

    And which two screw lugs on the relay are the normally-open circuit which I would attach in parallel with my separate millivolt stat's two wires?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,839
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    You have to find the coil of the relay and find the two coil wires. 1 goes to W, 1 goes to C
  • Motorapido
    Motorapido Member Posts: 307
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    You have to find the coil of the relay and find the two coil wires. 1 goes to W, 1 goes to C

    Understood, but I'm too much of a dummy to do this without guidance. Here's a pic of the Emerson 90-112 fan control relay center that I'm using. Can anybody make me a wiring road map?

  • HomerJSmith
    HomerJSmith Member Posts: 2,511
    edited January 2023
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    Here--Millivolt connections are RED & Black wires off the back of the relay, same pole. There are two poles on the relay.



  • Motorapido
    Motorapido Member Posts: 307
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    Here--Millivolt connections are RED & Black wires off the back of the relay, same pole. There are two poles on the relay.
    Thanks so much. I'm back in business. Really appreciate the wiring info.