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Thread: Help Wiring Honeywell T9 with No C Wire and Multiple Zones

  1. #1
    Junior Member

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    Help Wiring Honeywell T9 with No C Wire and Multiple Zones

    I'm looking at buying three Honeywell Home T9 RCHT9510WF thermostats, one for each zone. My current thermostats (Braeburn System, see wiring image) have RC jumped to RH (red wire), B (blue wire), O (brown wire) Y (yellow wire), W (white wire), and G (green wire). So there is no C wire, and as stated, three zones all of which control a boiler (hydroair system) and separate Rheem A/C system. (Two different compressors across three zones.)

    First question - Can the T9 be used with my current wiring?

    Next question - Can someone tell/show me the correct wiring to the T9?

    Thanks in advance,
    Joe A.
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  2. #2
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    As wired there are few thermostats that would work with your setup. No C wire but both O and B. Since you don't have a heat pump the O and B wires may not be in use.

    You need to go to the other end and see what the wires connect to. You should have a zone control panel where all the thermostats connect to.

  3. #3
    Junior Member

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    It will be very disappointing if I cannot use any smart thermostat.

    I called Honeywell support, and they told me to use the wiring below. Is it correct you think?

    Blue - use for common
    Brown - O
    White to - W2
    Red - R
    Yellow - Y
    Green - G

    They said based on existing wiring, I must have a heat pump. Just bought the house and don't recall the inspector saying anything about a heat pump, so will have to check into that. Thought it was just a boiler (hydroair).

  4. #4
    Senior Member

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    I don't think what they told you is correct. They used the thinking that if there is no C then B must be C. This is true for Trane and some others but the manuals for your thermostat show C in the end position where you have no connector. From that your B is likely truly a B.



    Trace the thermostat cable to the other end and see what wire is hooked up to what terminal there.
    Last edited by Stuff; 07-08-2020 at 11:38 AM.

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