Common wire not detected.

[WillieB]

My 3rd generation Nest thermostat was originally set up without using the common wire.  A few weeks ago it showed battery low and it shut off.  I have other units in my house that use the common wire so I thought that could help.  I had an HVAC technician out and made sure the common was available.  The common was connected to the base and when the thermostat was connected it said the common wire was not connected.  It was connected and the technician verified that there was a 24 volt circuit from the red wire to the blue (common) wire.  The blue wire is connected to the base but the thermostat is not getting power from it.  I switched the thermostat with one of my other units and it get the same error.  Also, the "failing" unit works when connected to another base.  It seems like the base is not making a connection between the wire connector and the pin connector.  Like I said I had an HVAC technician check everything and he installs Nest thermostats.  If I remove the common connector from the base I can get the unit to do basic functions but the battery is so low, it cannot connect to the network.

[Jhonleanmel]

Hi WillieB,

Thanks for posting ― let's get this sorted out.

A few questions: what Nest Thermostat do you have? Check this link to know what thermostat you have.

Best,
Mel

[WillieB]

3rd gen Nest Learning Thermostat,

Thankss

[Markjosephp]

Hello folks,

I wanted to stop by and see how I could help.

I appreciate your help here, Mel.

Thanks for letting us know, @WillieB. I'd love to know more about this.

To isolate:

1. Please check its power readouts under "Technical Info" settings and check for any wiring reports or message codes.
2. Are all your other thermostats the same model? If so, could you try connecting the non-working thermostat display to the working base and see if it's getting any power?
3. If it turns on, check the power readouts as well from the "Technical Info" settings.

Let us know how it goes.

Regards,

Mark

[Markjosephp]

Hello WillieB,

I'm checking back in. Were you able to do the steps above? I'd be glad to hear from you. I'd like to make sure everything is diagnosed so we can see what we can do.

Thanks,

Mark

[Markjosephp]

Hi WillieB,

It has been a few days since your last reply, and I am going to lock the thread within 24 hours. If you have any questions, please feel free to create a new post.

Thanks,

Mark

[WillieB]

The other thermostats are the same model and they do not get power thru the common on that base.  They do get it on their own base.  Also when I put the suspect one on another base it works.  Before you ask, yes there is power on the Common.  Had an HVAC tech double check.  

Regarding the tech check, with the common connected to the back plate it shows that there is no power detected. So it sees that the wire is there but not detecting a circuit.  Best I can tell the back plate has an issue. 

[Markjosephp]

Hello there,

Thanks for getting back to us and for updating us on what you've done to isolate the issue by swapping your two Nest thermostats. We'd like to take a closer look at this for you.

Please fill out this form with the needed information and let me know once you're done.

Regards,

Mark

[WillieB]

Form filled out.  FYI:

Display Software version 6.2-27 Serial number 09AA01AC381811QF Device ID 641666000092DC7F

BASE Software version 1.5.38/3.1 Model Backplate-5.4 Serial number 09DA02AC37181AHB

[Markjosephp]

Hello WillieB,

Thanks for completing the form; we have received it. Soon, a member of our upper team will contact you via email. Also, please continue the conversation there as this thread will be locked within 24 hours. 
 

Regards,

Mark

[WillieB]

Just posting to keep the thread alive.

[Markjosephp]

Hey there,

I've got you! I'll keep this thread open until you get assistance. Also, I will make a follow-up, so please be on the lookout for an email update.

Regards,

Mark

[Markjosephp]

Hello WillieB,

Thanks for your patience. It appears that you have already been assisted by our upper team. You can continue the discussion over email for more updates, as I'll be closing this thread within 24 hours.

Regards,

Mark