I recently purchased a new Thermostat with Wi-Fi capabilites for use in one zone of a two zone baseboard hot water heating system.

I pulled the existing thermostat (stat) to look at the wiring and only two wires were connected to the old stat, namely a red and white wire. However, there was a thrird green wire that was wrapped around the existing wiring that was unused on both the stat end and also at the boiler.

I believe that the unused green wire can be used as a c wire in the exisiting setup. I located the transformer and there looks to be both a terminal with an R next to it and one with a C next to it.

I've added a couple pictures of the wiring at the boiler. It seems each white wire runs to the respective zone valves (zone 1 and zone 2) and then are joined together to return to the R terminal on the transformer. The red wire from the stat is connected to the C terminal on the transformer (2 red wires - one each respective zone/stat).

Is the correct place to connect the green wire at the C terminal of the transformer where the two red wires also connect?

wiring diagrampicture 2

  • It seems like the green wires (C wires), should attach to the terminal labeled R on the transformer. But without seeing more of the wiring, or a schematic, I can't say for sure. – Tester101 Feb 5 '16 at 1:43
  • @Tester101 I took a photo of a diagram but looks like I'm not able to upload the image unless I edit my original post and delete one of the images. Is there another way to post the wiring diagram? – Rickydee Feb 5 '16 at 2:13
  • You could upload images to imgur.com, then post the link in a comment on this post. – Tester101 Feb 5 '16 at 2:22
  • Well it's simple enough. Normally, R is the line that goes from transformer to (old style) thermostat. Then stuff happens between thermostat and HVAC, and the electricity has to complete the circuit, so it comes back from the HVAC to the C line. Appears the installer put everything on the opposite pins from what it's labeled. Functionally it doesn't matter, it's AC. – Harper Feb 5 '16 at 16:38
  • @WolfHarper - so in this case teh Green wire would go to the R terminal not the C terminal since its reversed? – Rickydee Feb 5 '16 at 20:31

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