I have a Nest Learning thermostat. Recently, it has caused a clicking sound to emanate from the furnace area whenever the system is powered off. I've determined this is due to the thermostat drawing insufficient power through the W1/Rc wires that it uses (2 wire heating-only system). Nest technical support recommends connecting a C wire, although I am also investigating if this is a possible battery issue. We are running our system for 1-2 hours a day, and our electrical parameters on the Nest device are all within the ranges recommended here: https://support.google.com/googlenest/answer/9241211?hl=en#zippy=%2Cpower
As I'm seeing a lot of recommendations to connect a C wire regardless for smart thermostats, I'd like to see if that is possible in my system. I do have 5 wires pulled through. I have taken pictures of the thermostat wires, along with the control board setup: https://photos.app.goo.gl/6zJfUfQsRQ2cDoTq6
Can anybody tell me if there is some way I could connect the loose blue or yellow wires to the board so that either one could function as a C wire?
Best Answer
I'd get a "piggyback" crimp connector and use that to land the common C wire on the C terminal
Given that your board does not supply outgoing C terminals, we have only one sane place to tap C left, and that's at the terminal where it comes into the board from the transformer. However, we still need to be able to connect the incoming C wire to that terminal, so you'll need to use a ¼" "piggyback" crimp terminal rated for 18AWG wire crimped onto the end of the common C wire in your panel to leave room to land the C wire from the transformer (it'll look like the one shown below):