I have a pretty old American Standard GPMX - 6r boiler that I inherited when I purchased the house. It had a 2 wire thermostat hookup, but I found for my new thermostat, I need a 3-wire. It needs to be attached to the common. I ran the new wire, but I want to know where to find the common terminal at the boiler. Can't find instructions for it. I am pretty lost.
Thanks for you help.