Wiring assistance

[anatali]

i recently purchased a home that has two furnaces. I had a Nest thermostat E at my previous residence and wanted to continue to use it as well as get a second one since there are two furnaces and two thermostats in my new house. I bought a new one and replaced one thermostat without issue. When I attempted to install the second one the existing thermostat I was replacing seemed to be slightly differently than the one I had already replaced, although the available wiring in the wall seemed to be the same. I decided to install it as I had the other unit. When I attempted to test it is sounded like the furnace was trying to fire up unsuccessfully. I could hear it "power up" and then quickly "power down". It kept cycling like this. I decided to try only using the wires that were hooked into the previous thermostat and that also did not work. I decided to reinstall the old unit as it was and once this was complete the furnace fired up without issue. Can someone help with wiring this? I cant seem to include pics in this post? I do have them.

[anatali]

Guess I couldnt include them in my first post. First pic is how the trouble thermostat was wired. Second pic is how I wired the first thermostat that worked but did not work for the one in question. Third pic is how that first thermostat was wired before I replaced it.

[Markjosephp]

Hello anatali,

Congratulations on your new home, and it's great that you're looking to set up your Nest Thermostats. It sounds like you encountered a challenge with the installation of the second thermostat, and I appreciate your effort in troubleshooting.

To assist you better, let's try to identify the issue with the wiring. While you can't include pictures in this post, you can provide a detailed description of the wiring setup for both thermostats. Also, make sure that the wiring on the second thermostat matches the compatibility requirements for your furnace.

If the wiring seems to be consistent and the issue persists, consider checking the Nest Thermostat's compatibility with your specific furnace model. Additionally, double-check the configuration settings on the Nest Thermostat during the installation process. Sometimes, adjusting settings related to the type of heating system and the presence of multiple furnaces can resolve issues. To insert an image in a post:

1. Reply to this post.
2. Click Insert Image (camera icon).
3. Choose an image source location.
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If the problem persists after trying these steps, 


Best regards,
Mark

[anatali]

Are you able to see my reply to the original post? I included pictures.

[Markjosephp]

Hi there,

Whoops! Thanks for the photos. Could you try removing and leaving the C wire disconnected? Then, gather the power readouts in the Technical Info with and without the C wire connected.

Keep me posted.

Best,
Mark

[anatali]

Sorry for the delay in replying.

The first two pics are the power readings with the C wire attached. The second two are without. The fifth pic is an error I encountered. I dont understand why it said the R wire was not attached....it definitely was. When I turned the power back on it let me cycle through the menu for a bit and then threw the error. I decided to cut the R wire and strip it to start fresh. I rehooked it up and the same thing happened. I don't know what to do about this. What am I looking for in the power settings? Anything you can offer I appreciate.

[zoeuvre]

Hi anatali, 

Chiming in—your thermostat reads below 24 V with or without C wire connected to it. In this case, we can conclude that the reason for the error is that the C wire is not properly grounded. Therefore, I highly recommend a Nest Pro or technician to either fix or reinstall the wire on the control board.

Thanks,

Zoe