topic Re: Gen 3 Learning Nest- no power through any wires in Nest Thermostats

Gen 3 Learning Nest- no power through any wires

ColoradoYeti — Thu, 10 Mar 2022 17:15:23 GMT

I tried to install my nest on my own, but I received an E74 code- no power to Rh line. I have an Rh and a W1 line going into my thermostat, and I believe they are called COM1 and H1 on the furnace side. I followed all the troubleshooting steps I could find with google, and it resulted in telling me the issue was on my furnace side. I worked with Google chat to confirm that everything was compatible on paper. (case number: 8-2394000032432)

My next approach was to have OnTech come out to diagnose and fix the issue. They arrived this morning and spent a good bit of time in my crawlspace looking at my boiler. Their diagnosis was that there were no lines sending power and that it was an incompatibility issue. I asked if the google C-adapter would work, but since there is no power to any of the lines, this would not solve my problem. I also asked about providing a tertiary C wire from a plugin adapter (common for a doorbell) and both he and his friend (an HVAC specialist) did not think that this would solve my issue either.

What are my options here? I would really like to convert to my nest thermostat and not give up, as my current thermostat is just eating up batteries and requires reprogramming all the time.

Re: Gen 3 Learning Nest- no power through any wires

Patrick_Caezza — Fri, 11 Mar 2022 02:09:44 GMT

So you have two wires coming from your boiler, a red and white one?

Lots of times a boiler is just looking for a switch closure and the Nest thermostats can't provide that by themselves, but they can if you add a simple relay and an external 24V transformer.

Here is a simple diagram of how you can probably make it work.

Re: Gen 3 Learning Nest- no power through any wires

Ryan_G — Wed, 16 Mar 2022 03:46:13 GMT

Hey ColoradoYeti,

Thanks for posting here in the Google Nest Community Forum.

Have you tried the recommendation from Patrick? Let us know how it goes by replying to this thread.

Thanks for your help, Patrick.

Best regards,

Ryan

Re: Gen 3 Learning Nest- no power through any wires

ColoradoYeti — Thu, 17 Mar 2022 01:45:10 GMT

Hey Patrick, I just received a 24V transformer and the relay that you referenced.

I am a little confused about your diagram... how do I connect the 1 wire to the nest and the relay? Do I need a long jumper line from the relay as line 3?

Re: Gen 3 Learning Nest- no power through any wires

ColoradoYeti — Mon, 21 Mar 2022 15:02:05 GMT

I added the external 24V power supply, and no further hardware or cables were required. The thermostat works as designed.

Re: Gen 3 Learning Nest- no power through any wires

aatienza — Tue, 24 May 2022 06:40:56 GMT

Hey ColoradoYeti,

Thanks for letting us know! You can reply to this thread if you have other questions, we're here to help.

Thanks,

Archie

Re: Gen 3 Learning Nest- no power through any wires

aatienza — Wed, 25 May 2022 06:42:37 GMT

Hey ColoradoYeti,

As we got our resolution here, I'm going to mark this one as resolved. Please feel free to open up a new thread if you need assistance.

Thanks,

Archie