Can not get the Common (C wire)to be recognized by Nest Thermostat?

[Tazman]

My new Nest Thermostat is not detecting the Common (C Wire)?  But, the system is working.  I'm concerned this may be a problem down the road and wanted to get some feedback.  I also have a built in humidifier on the heating system, and I'm wondering if that is the cause.   I've also double checked and have made sure I have a good connection with the existing C wire and the Nest thermostat.  Any advice would be welcome.

[CoolingWizard · Accepted solution]

If the nest is not detecting the Power Common, it is possible it is not connected at the air handler end.  

Ken, The AC Cooling Wizard

[CoolingWizard · Accepted solution]

If the nest is not detecting the Power Common, it is possible it is not connected at the air handler end.  

Ken, The AC Cooling Wizard

[Tazman]

I think you are correct, it's new construction and I think it was installed incorrectly.  I had an issue with the humidifier as it was constantly running, not just when the fan was running.  HVAC man came and fixed that....do you think that may have something to do with the loss of power on Common?

[EdwardT · Accepted solution]

Hi folks,

@CoolingWizard, thanks for the help!

@Tazman, how's it going with your Nest Thermostat? Still need our help?

Thanks,

Edward

[AbigailF]

Hey Tazman,

Checking back in should you still have some questions here. Let us know by replying to this thread. 

Best, 
Abi

[AbigailF]

Hello Tazman,

We haven't heard from you in a while so we'll be locking this thread if there is no update within 24 hours. If you have any new issues, updates or just a discussion topic, feel free to start a new thread in the Community.

Regards, 
Abi

[Tazman]

Problem was solved, as the common wire was not connected at the furnace side.  Technician come out to fix.  I was surprised to find out that most installations do NOT connect the common wire unless they know you have a smart thermostat.

[Markjosephp]

Hi Tazman, 

I appreciate you posting and updating us on your efforts to address your concern and how you figure it out. Hats off to you!

So we can consider this one complete, and I will lock the thread within 24 hours unless I can help out with anything else.

Regards,

Mark

[CoolingWizard]

If your common wire was working before the HVAC technician worked on the Humidifier, then yes, it appears that the repair disconnected your common wire. If the the wire connected to the C has never worked, it might just need to be connected to the power common in the air handler. 

Ken, The AC Cooling Wizard