Hi folks. Similar problem here. I have three wires, red, white and green. No spares available. Here is a pic of the wires at the zone valve and the thermostat has red, white and green, but green is not connected to anything on the other end.
All four zones have their whites and greens connected. Can I make this work? No fan BTW…just baseboard heat.
This is a taco zone control valve… do you have a picture of the transformer that feeds this valve, and the associated wiring? There are a few different ways of wiring these up, and I need to see which way your system was wired before making a recommendation.
Any help @speadie with installing the thermostat to an ac system that has 3 wires only on the control board and two wires going to what I assume is the coming from the outside ac unit?
Control board:
Figured it out.
Such a helpful thread!
I’m in a similar boat. Only RWG wires were visible when I opened my old thermostat. The furnace did have a blue and yellow (in pic) , but they were coiled away and not going anywhere (at least I think not).
Any help would be greatly appreciated. (thermostat pictured below)
Check in the wall behind the thermostat for a blue or yellow wire. If you find a blue wire, then it can be your C wire, just connect it to C on your furnace and C on your wyze (but make sure the power is off first, you don’t want to blow the fuse.)
Thank you @speadie! The other two wires were indeed hidden behind the old thermostat and took a bit of prying to get out. Wyze thermostat is working perfectly now.
Appreciated 
