My home is 3 zones (2 hot water, 1 steam) and heated with oil. I added a Nest Thermostat E to one of the zones and while it does work without the 'C' wire, I would like to wire it anyways so my relay stops buzzing when the Nest is powering itself. All of my thermostat wires have 3 conductors and since I have no air conditioning here, I believe I can use the unused 'Y' conductor.

I have 2 zone relay valves (Honeywell 8043F1036) and I'm not certain where the common wire is on this relay.

enter image description here

I believe it is either wires 1 or 2 labeled in the picture. The wiring diagrams on Honeywells website aren't clear which terminal is common, or if it is even one of these terminals.

2 Answers 2


According to the wiring diagram I found, typical wiring is as follows.

Honeywell 8043F1036 Wiring

  • 1 END SWITCH (To circulator or another valve)
  • 2 END SWITCH (To circulator or another valve)
  • 3 TH/TR (Thermostat and Transformer)
  • 4 TH (Thermostat)
  • 5 TR (Transformer)

You'll have to verify this is how your valve is wired, but it looks just like the diagram to me. If this is how it's wired, you should be able to connect the c wire to the TR (5 in your image) terminal on the valve.

  • 1
    My system was wired exactly as you mentioned. The two thermostat wires were wired backwards in my old thermostat. This didn't matter for a simple mercury switch unit, but I had to reverse the R & Y wires on the Nest to get it working correctly. Working great now.
    – Seidleroni
    Oct 19, 2017 at 20:14

Every transformer has 2 terminals on the 24V side.

One of the terminals is R, and that already goes to the thermostat.

The other transformer terminal must necessarily be C.

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