View Full Version : Tstat Common Wire

11-12-2007, 09:04 AM
i want to install programmable thermostats. one each for the upstairs and downstairs zones in my 2000SF raised ranch.

right now i have the basic honeywell round tstats.

the one downstairs has two wires which are not labeled. the upstairs handles AC and heat and has the following wiring;

separate wires to R and Rc with an additional jumper wire between the same two terminals. Also, W, Y and G.

I have 2 Taco zone valves (3 terminals) and no C wire (constant)to either tstat. However, i would like to use the extra wire already installed at each tStat which is not connected to anything to bring constant voltage to be used for the new programmables.

Could you tell me where i need to hook to at the boiler/transformer end to get the common voltage to power the new Tstats?

i could get pics of the wires if needed...