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C wire with Honeywell V8043F?

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sameguy
sameguy Member Posts: 3
We have a boiler with 3 zones of hydronic heating in our house. Wife wanted smart thermostats so I got some inexpensive Amazon Smart Thermostats. Ther require a C wire for constant power. There is an extra wire at each thermostat, but at the Honeywell V8043F where they are connected the third wire is not connected to anything. I have looked at a wiring diagram for the Honeywell V8043F and see there are 2 wires that go to the low voltage transformer. Can I connect the 3rd wire to one of those for constant power?

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  • Robert O'Brien
    Robert O'Brien Member Posts: 3,542
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    TR terminal
    To learn more about this professional, click here to visit their ad in Find A Contractor.
    STEVEusaPAsameguy
  • sameguy
    sameguy Member Posts: 3
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    Thank you sir, very much appreciated!
  • EdTheHeaterMan
    EdTheHeaterMan Member Posts: 8,153
    edited October 2022
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    The C wire is not the only important wire to connect to the proper terminal on the new thermostat. You must connect the R wire to the proper terminal on the thermostat also. With a 2 wire setup there is no problem reversing the wires. When a Common is required then the R from the thermostat MUST be connected to the R on the transformer.


    In this picture, to make things easier, I would use the unused white wire to connect W on the thermostat to the terminal you indicated as #4. Then I would use the Red wire to connect the R on the thermostat to the terminal you indicated as #3 (as it currently is). I would then connect the disconnected Black wire to C on the thermostat and #5 on the zone valve.

    Edward Young Retired

    After you make that expensive repair and you still have the same problem, What will you check next?

    zvalvesameguy
  • sameguy
    sameguy Member Posts: 3
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    Edward, thank you for the clarification.