C-Wire for new T-stat

Steve Garson_2

I have a new (old) home with the old Honeywell round t-stats. I would like to install a set-back t-stat that requires a c-wire. Looking at the zone valves in the basement, I can see that only two wires are used. The green wire is not connected. Obviously, the same is the case at the t-stat location.

When do I connect the green wire to provide the c-wire at the new thermostat? The boiler is a WM GV-5.

Thanks,

Steve
Denver, CO (previously Boston)

Alan (California Radiant) Forbes

Hi Steve:

Many set-back thermostats don't need a c-wire, but it sounds as though yours does. Double check.

You could possibly find a c-wire on your boiler, but I would stay away from that option since you could accidentally short out the transformer which may mean having to replace the boiler's circuit board.

The best option is to install a zone valve controller that has a c-wire connection available as does Caleffi or Taco. Caleffi is shown here:

https://s3.amazonaws.com/s3.supplyhouse.com/product_files/ZVR103-submittal.pdf

You will have to re-wire your zone valves and your boiler end switch. Easy if you've done it before; a weekend project if you haven't.

Steve Garson_2

I think I'll simply buy a different T-stat. Thanks for your response. Steve

Tim Potter

I powered my Emerson Sensi with an external wall wart for my "no c wire" application

https://sensi.emerson.com/en-us/support/adding-a-24-vac-external-transformer

https://www.homedepot.com/p/Emerson-Sensi-Wi-Fi-Thermostat-for-Smart-Home-ST55/301231478


Tim