On Monday, October 20, 2014 11:03:16 PM UTC-4, wrote:
On Mon, 20 Oct 2014 18:32:01 -0700 (PDT), Mikepier

wrote:



Hello. I currently have a Honeywell standard display T-stat. It has only 2 wires connected to the R & W terminals to control my Weil-Mclain steam boiler. The T-stat is battery operated.



I have spare wires in my current T-Stat wiring which I would like to utilize to hook up a Wi-Fi T-stat. The Honeywell rep I spoke to in tech support said to put the 2 existing wires to the R & W terminals, and to connect a separate 24VAC Power source ( which I have in my basement) to the C & RH terminals, with all jumpers removed.



Just wondering does this sound correct?



Your stat is operating as a simple 2 pole switch. The Red is 24v in

and the white is "heat call" out. The common is in the boiler.



You could use an unused wire to bring the common to the WiFi

thermostat from the transformer, hook it to C and you are done.


+1

As you say, the only thing it needs to power a smart thermostat is
one additional wire to the common. And as Tony said, the instructions,
which should be available online should confirm that.