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New Bluetooth Thermostat for hot water heating system

DiloDilo Member Posts: 5
edited January 11 in THE MAIN WALL
Need help wiring a new thermostat at the furnace. Have an oil burner, hot water system. (No A/C). The old thermostat has the red & white wires hooked up. My thermostat WIRE has 3 wires - the green one is not being used. *See first photo below*.
My new bluetooth thermostat requires 'C" wire, so I used the green wire for that purpose. I hooked up the C, red and white wires to the new thermostat, and on the furnace- end of the wire, I put the green wire on a dedicated 24v terminal, leaving the existing red & white wires as is. The thermostat would not power up.
I then moved the red thermostat wire on the furnace, to the Common terminal, leaving the white wire as is. This made the thermostat flash on and off. **(See photo 2 (attachment below) of the furnace circuit board - I circled the C wire at the top (currently unhooked), the 24v & common terminals, and the thermostat wires in question (zone 3)
Finally. I then moved the white thermostat wire to where the red wire was. I got full power and functionality to the thermostat. Was able to program it, and even link it to my smartphone. The issue is that it would not turn the furnace on. It confirmed the heat was activated, but no heat flowed in that zone. I feel I am close with the wiring, but just not 100% there yet. (I had also tried running a jumper wire from the common to the red thermostat terminal, with no luck). What do I need to rewire in the furnace to get this working? Thanks for any professional insight you can provide. (email is [email protected], if needed)


  • IronmanIronman Member Posts: 6,142
    edited January 11
    You have "R" and "W" reversed on the zone panel. "C" goes on "common" there. The stat in your pics has no "common" terminal.

    Also, using a setback thermostat with hydronic heat will provide little or no energy savings at the cost of decreased comfort. Unless the the setback is gonna be for days, not hours, set it to one temperature and leave it there.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Jamie HallJamie Hall Member Posts: 14,797
    You have what you need -- 3 wires. In your old system, it didn't matter which of the two wires was white and which was red, at either the thermostat end or at the control board end -- and electricity is colour blind. However, in your new system it does. C needs to go to the common return on the control board. One of the two terminals for that zone on the control board will be power -- 24 vac. The other will not. R on the thermostat needs to go to the powered terminal, and W on the thermostat needs to go to the unpowered terminal. As @Ironman said, try swapping the R and W wires on the control board.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.
    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • DiloDilo Member Posts: 5
    I uploaded a better photo of the furnace wiring. (Still getting used to this site).
  • DiloDilo Member Posts: 5
    OK, I think I understand, but want to clarify, to be certain. After all, it is 35 degrees here now, so I don't want to harm the furnace in any way.

    1. Green "C" wire on t-stat goes to "Common" terminal on furnace.
    2. Red wire from t-stat goes to 24v terminal on furnace
    3. White wire on T-stat goes to either of the T-stat terminals on furnace.
  • IronmanIronman Member Posts: 6,142
    No, "Tr" goes to "R" on stat; "Tw" goes to "W" on stat; "common" on zone board goes to "C" on stat.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • DiloDilo Member Posts: 5
    OK, thank you so much for clarifying. I am at work now, so will re-try tonight when I get home. Will advise. Thank you!!!
  • DiloDilo Member Posts: 5
    You guys rock! Hooked it up as you indicated, and everything works perfectly. Thank you so much!

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