I want to upgrade my old mercury thermostat that I currently have to a newer programmable thermostat. This little DIY project is for my first late 1920's home that I recently purchased. I currently only have heat hooked, and use window A/C's, however I have no problem running a 18/5 Cable down to the boiler instead of a 18/3.
My question is how to I the C wire from the boiler transformer.
Please see pictures attached from the manual for the boiler (I have no idea why they even have 3 listed). Currently the two cables that run from the thermostat are hooked up to T-T terminals (on the top of the figures that run from TH-2).
Would all I need to do is basically run a third cable to the empty C terminal in N-H-C-W-B terminals on there?
UPDATE: The physical boiler has a Honeywell AT150D1001 transformer attached to it[next to the emergency cut-off switch]; which seems to be supplying the 24V to the system.(See picture below). My question now becomes do I use the white wire or the dark brown wire as the C wire that I run to the thermostat?