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C terminal on Crown Boiler?

eclark0013
eclark0013 Member Posts: 3
in Strictly Steam
I am trying to figure out where the c terminal is on this boiler. I'm new to the home and the boiler is only 5 years old, used for steam radiators. I figured it would be compatible with a Nest thermostat but now I am not so sure. This is the side of the boiler

And this is where it appears that the thermostat wires are currently connected.

The wires (which are R and W on the nest) are connected to R and B, leaving an open W. So does that mean that the W on the thermostat goes to the B here? And if so is the open W actually a C? It feels like a mess to me. Appreciate any guidance. Thanks!

Comments

  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,495
    Can you take a picture of the wiring diagram that is on the side of the boiler and post it here? The electrical box on the upper left of you picture looks like a transformer. The C wire would start there.
    eclark0013
  • Jamie Hall
    Jamie Hall Member Posts: 24,876
    And a caution: the Nest is only marginally compatible with steam or hot water heat. You will have to disable almost all its automatic and "smart" functions to get it to work even marginally well.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    eclark0013
  • eclark0013
    eclark0013 Member Posts: 3
    Here are some pics of the diagram


    And is this the part you were saying is the transformer? I took the cover cover off and there was a slew of wires but no clear labeling. It seemed unwise to try to get into that inner box without really knowing what I was doing. Thanks!
  • eclark0013
    eclark0013 Member Posts: 3
    @Jamie Hall , the goal was only to be able to change it from my phone. I had no intention on using any of the "smart" functions. I did not get the "learning" thermostat. Just their most basic one. Is there more functionality that needs to be disabled, and if so, would you know more about how to do that or any suggestions on how I could figure that out?
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 16,495
    You need 3 wires from the boiler to the thermostat. If you have that you can hook up the Nest.

    1.The "C" wire you are looking for is the "yellow" wire coming out of the transformer. According to the diagram there are 4 yellow wires and 1 red/yellow wire spliced together coming out of the transformer. You add the C wire coming from the nest terminal "C" to that group of wires.

    2.The red wire on the Nest "R" terminal should connect to the BL wires coming out of the transformer (I don't know if BL is blue or black) It's probably Blue.

    3. The W wire on the Nest gets connected to the BR (brown wire that goes to the coil of the Honeywell R8225B relay.

    You can find the transformer , the relay and the thermostat in the last picture you posted.


    remember electricity is color blind. You can use any color you want as long as it is connected to the correct spot on both ends
    eclark0013

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