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Good morning. I have an old Teledyne Laars JVT-100C Boiler, that only has R,W,A terminals. is there a way to add a C wire to this boiler in order to power my thermostats?

Thanks in advance...

  • Can you post a wiring diagram for your boiler? – ThreePhaseEel Feb 18 at 17:18
  • i can try when i get home tonight.. but it doesnt look like i can upload images here... – Brian Ciarcia Feb 18 at 18:01
  • There's a button that looks like a stylized painting in the post editor that will let you upload images – ThreePhaseEel Feb 18 at 19:23
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Yes you can, on your boiler there is a transformer above the gas valve. One terminal is the 24 v supply and the other is the common. It's not always easy to identify which is which. The process involves connecting one side of the secondary to the L2 (neutral) and checking if voltage is additive or subtractive. Hopefully it's identified. It's much easier that way.

  • thanks for the response.. i should have searched first.. :) i see others had the same question.. so it looks like the bundle of yellow wires would be the common, that i can tap into. since i dont have an aquastat, could I just bring the yellow to the A terminal and then run the wire from there up to my thermostats? does that make sense??? – Brian Ciarcia Feb 18 at 16:18
  • I'm not sure what the a terminal is but if it's just an empty spot then yes it's fine. I would re identify it as common so anyone down the road knows, and doesn't fry it. – Joe Fala Feb 18 at 16:31

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