I have a hydronic heating system (Lochnivar)that came controlled with an older (dumb)enter image description here thermostat. I have 5 wires behind the wall and 5 wire in the wire packet going into heating system however only the red and white wires are connected on both sides. The remaining wires (Yellow, Green, Blue) are not connected on either end.

I'm installing a smart thermostat that needs a C-wire, where can I connect that on the circuit board of my system (picture attached)? Any advice appreciated.

  • Is there an air handler (fan coil) in your system, or do you have radiators/baseboards/underfloor heat only? Commented Sep 13, 2020 at 0:41
  • 1
    No air handler, no AC, the underfloor heating (hydronic) is all that's here.
    – Matt
    Commented Sep 13, 2020 at 0:43
  • What model is your boiler then? Commented Sep 13, 2020 at 0:45
  • It appears most similar to this one but I’m not able to locate a model # anywhere lochinvar.com/products/residential-boilers/noble-boiler
    – Matt
    Commented Sep 13, 2020 at 1:16
  • Hm. Looking at the install manual for the Noble doesn't give any clues either... Commented Sep 13, 2020 at 1:40

1 Answer 1


Nowhere in there. that's a DC circuit and a "C" wire is an AC thing.

you'll need to use an auxillary power supply to run your smart thermostat.

  • Thanks for the answer. I've located a simple auxiliary power supply that plugs into the wall, will post when I confirm the solution
    – Matt
    Commented Sep 13, 2020 at 21:58

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.