E79 No power to C wire

[rbrychckn]

My Nest Learning Thermostat has been working for a year now, then we had a power outage in our house and the furnace that is supplying 2 Nest Learning Thermostats both now show a E79 error.  

The circuit breaker did not trip.  There is a zone panel on the side of the furnace that is receiving power.  Since it was both thermostats, I assume that power is truly not running to either thermostat.  Of note, a 2nd furnace with another thermostat is working fine after the power outage. Can anyone offer any advice?

[bossmonkey]

I just had this exact same error message on my Nest thermostat. I pulled the display cover off the wall, then attached it back on and it works just fine now.

[Jake]

Hey there,

Thanks for the helpful reply bossmonkey.

I wanted to follow up and see if I could be of any help. If you are getting an E79 error, no power is detected to your C wire. I found an article that has some troubleshooting steps. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further. 

Best regards,
Jake

[WAON]

I have the same problem every couple of days (sometimes more than once in the same day). Pull off and reattach and all is fine. Getting really frustrated with it. I’ve pulled the C wire, straightened and made sure it’s clean. Heat continues to function thankfully.

[rbrychckn]

Thanks to all.  I just flipped the switch and the breaker twice and power was restored.  Not entirely sure why it worked, but it did.

[Jake]

Hey there,

I am glad to hear everything is working properly from here. I wanted to follow up with you, and see if you had any questions from here. Please let me know, as I would be happy to take a closer look.

Best regards,

Jake

[WAON]

Jake,

im still having to remove and replace the thermostat every couple of days to clear the E79 error. Not sure why it keeps happening.

[Jake]

Hey WAON,

I am sorry to hear you are still running into the issue. Do you mind me asking if you have tried to double-check the wire at the control board on your HVAC system? Does everything seem connected properly? 

Best regards,

Jake

[Jake]

Hey there,

I wanted to check in and see if you are still in need of any help. Please let me know, as I would be happy to assist, and answer any questions you may have.

Best regards,
Jake

[Jake]

Hey there,

I wanted to check in, and let you know that I will be locking the thread in 24 hours. 

Best regards,

Jake