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Heat only Wiring Question / Replacing honeywell battery thermo

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  • Heat only Wiring Question / Replacing honeywell battery thermo

    Hello all, I have a Wired Insteon thermo that I would like to replace my current Honeywell battery powered themo...

    I have a boiler / no tank > Hot Water radiant heat (not a heat pump)

    Currently my wiring situation:
    5 Wires in the wall
    Behind current thermo plate I have a Red and White wire attached to R and W...These two wires I have traced to my basement where they are pigtailed to a cable that is coming from the boiler, inside the boiler the red wire is attached to a connector that shares a much thicker red wire to something else inside, the white wire is connected to a single connector on the same control unit.

    I also have a honeywell 24v transformer in the basement where the 5 wire cable ends...that has 2 terminals on it R and C, these are both hooked to Green and Yellow cables of the 5, the blue wire in the 5 line is not used.

    From what I gather from reading that 24V transformer R is Hot and C is Common/Neutral (also above R terminal/post is say "Load")

    My question is Can I use Red and White from Boiler to the termo 24R and W1, then connect my 24V C line from the transformer to the thermo on 24COM? Leaving the 24V R post / wire unused from the transformer?

    Or should I connect both from the transformer C to 24COM and R to 24R on the thermo and only use the white wire from the boiler to the W1 on the thermo?

    Just don't want to mess up any of the boiler boards, I care less about possible thermo damage if I am wrong.

    Any help would be appreciated, thank you.

    -Derek

  • #2
    Anyone else that may have a similar scenario...I was able to get it working, below is what I did.

    I found I could not use my stand alone 24v transformer, What I had to do was take my Red Wire > 24H | White to W1 | But since I did not have a 24COM wire (except from the external transformer) I had to open up my boiler / furnace (gas) and tracked down where the Red and White where going from the thermo wiring...From there I found a Blue common wire on that transformer internally and used a new piece of wire to go from that to my 5 wire setup in the wall and pigtail it... That allowed me to extend my common from inside my unit to the thermo.

    Once I did this everything worked great.

    FYI, my unit Red wire was producing 26V on my multi-meter, so I called insteon support first and asked if what I was doing would be ok on the thermo since it was rated @ 24V and not 26V... they checked and confirmed that 24V is just the minimum but can be higher without causing any issues. The transformer plate inside was stamped 25V @ 40AMP... but read @ 26V.

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    • #3
      Most of those transformers put out a higher voltage because of voltage drop that will occur once you add the length of the thermostat wires to the circuit. Your reading is normal.

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      • #4
        Originally posted by SteveL View Post
        Most of those transformers put out a higher voltage because of voltage drop that will occur once you add the length of the thermostat wires to the circuit. Your reading is normal.
        Good to know thank you.

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