Williamson Gsa-125-N-IP C wire help!

JohnnyZoo

Hey all,

So my Nest thermostat started giving me power issues after almost a year. I was running it only on two wires, but I think I need to connect a C wire to it as well. Currently there is a wire ran from the thermostat to the boiler, but is not connected to anything in the boiler itself. Can I simply take the 24v green wire that is screwed onto the furnace and connect it directly to that wire, or do I need to connect to another interface in the furnace itself? Any help or insights are appreciated!

HomerJSmith

Maybe, to your question. If you have an extra unused wire coming from the thermostat to the control board, do this, connect the extra wire at the thermostat to the C terminal on the Nest and connect the extra wire at the circuit board to the C connection that you see on the Ladder Wiring Diagram. You can connect to any point that is connected to C on the Ladder Wiring Diagram. That would provide power to the charging circuit in the Nest. R power in, W power out, C charging power out to the Common on the transformer. Make wiring changes with power off to the heating unit. I see that the Common on the transformer is grounded, but is it grounded to the chassis? I wouldn't take the chance without VOM measurements.

How is the Nest currently wired? What terminals?

JohnnyZoo

the Nest is currently wired at the W1 and RH terminals, which go into the furnace on the red and white wire, which are connected into the yellow and green terminals on the board (I’m guessing this is wired incorrectly now as well?)

The board seems to be mounted sideways I think and the C I should splice into shouldn’t matter as long as it’s connected into that bundle that’s mounted on the top left? I just wanted to make sure since there are so many connections going into that terminal, it doesn’t matter which wire of the group I splice the new thermostat wire into.

STEAM DOCTOR

You can tap into the black wire, coming off the "C" on the fan relay.