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No C wire, no easy way to use a power adapter--is there any Nest that will work with my old boiler?

amhz
Community Member

I have a two-wire heating system running my gas boiler and radiators. I bought a 2020 Nest, and quickly found out it doesn't work without C wires (which my system doesn't have). I purchased the Nest Power Connector, and then began looking for the wire terminals on my boiler, which were nowhere to be found. I finally figured out that they are in a junction box on the ceiling. It's a rats' nest of unlabeled wires, although I think I can figure out which two are connected to my thermostat based on the colors. My next realization: I cannot find a single electrical outlet near this ceiling box. I'd have to pay to put in a new outlet to use the adapter which I'm not even sure will work with my system. I'm attaching pictures of the junction box.

I've read mixed reviews about using a 3rd generation learning thermostat without a C-wire, including many reports that battery issues make the thermostat impossible to use long-term.

Appreciate any advice.

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7 REPLIES 7

Houptee
Silver Product Expert
Silver Product Expert

The blue and yellow are the 24 volt AC.

I can't tell which one is connected to red but the other one is common.

So if you can pull a new thermostat cable use 5 conductor wire and use red white and blue at nest blue will be common C.

Then connect blue to to the transformer wire nut which ever is not hooked to the red. I would not use the nest power device just run a new thermostat cable if possible.


Houptee -- NJ Master HVAC Licensed Contractor

amhz
Community Member

Thank you!!

Jhonleanmel
Community Specialist
Community Specialist

Hey folks,

We appreciate your help here, @Houptee.
@amhz, I wanted to follow up and see if you are still in need of any help. Please let me know if you are still having any concerns or questions from here, as I would be happy to take a closer look and assist you further.

Thanks,
Mel

amhz
Community Member

Thank you, Mel. I have to figure out if I can fish a new thermostat wire through the wall on my own to make this work. If you have advice beyond what @Houptee generously shared, let me know. Otherwise, I'll give this a go.

Jeran
Community Specialist
Community Specialist

Thank you for helping out on this thread, Houptee and Jhonleanmel!

Hey there amhz,

I'm just checking up on this thread, do you have any more questions or need any additional help? 

Best regards,
Jeran

Jhonleanmel
Community Specialist
Community Specialist

Hi folks,

Chiming in to see if you still need assistance with this. Let us know if you have additional questions ― we'd love to help.

Best,
Mel

Hi everyone,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.

Thanks,
Mel