Wiring noob here. Can someone give me step-by-step instructions for where and how I should attach a C (common) wire to a Triangle Tube Prestige Excellence 110 boiler for a ecobee3 thermostat?
I think the gray box on top (pictured below) with the blue, brown, red and white wires is the 24VAC transformer, but I'm not sure.
Also I'm not sure where or how I should connect a C wire.