Thermostat Question

Old 03-30-06, 03:21 AM
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Thermostat Question

I have a peerless boiler with 3 zone valves. Each zone valve has 3 wire running to a thermostat and they are connected to R,Y,W. I recently installed a Honeywell RTH7500D programmable thermostat. Everything works great. It is running on its battery because I have nothing tied to the C terminal on the thermostat. The cable going to the stat has only 3 wires and it would be very difficult to run another cable from the garage (Where the 24v originates). My question is, is the C terminal (common on the 24v transformer) the same as ground? Can I just tie C to the ground of a near by recepitcal? If not, Should I just put a 24v transformer in the attic and disconnect the jumper between RC and R and hook the secondary transformer to RC and C? Thanks for the help.

Last edited by HTRK-1; 03-30-06 at 03:53 AM.
Old 03-30-06, 05:22 PM
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Do not hook the common to a recpticle. I don't know how well the second transformer idea would work. Why not continue to use batteries? My thermostats run only on batteries & I only have to change them once a year, max. My question is what kind of zone valves do you have which require 3 wires to the thermostat? The only valves I've ever seen like this were old Honeywells which required power both to open (R-W) & close (R-Y).
Old 03-31-06, 03:21 AM
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I will look at the brand name on the zone valves. They are wired "series 20" according to manual that came with the thermostat. I have 4 thermostats in the house 3 zones of heat and one AC. I wanted to extend battery life as long as I could. I've done some more research and it looks like the the secondary transformer is the standard fix for my problem as long as I'm not using the cooling side of the thermostat, I can remove the R to RC jumper and power the stat through RC and C. I ordered a honeywell control transformer and will run thermostat wire to all the stats from it (the A/C stat may already have a common, I haven't looked). Thanks

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