Random E:80 and E:74 Errors

[bchambers]

Hi! I'm new to the forum and hoping that someone in the community can provide some guidance and/or assistance with an issue with the Nest Thermostat (Model Display-3.4) that I noticed a couple of days ago.

When accessing the thermostat via either the app or the thermostat itself, we are getting random E:80 and E:74 errors.  They appear intermittently and only remain for a short period of time before the thermostat returns to normal operation (shows no errors, etc.).  

It's difficult to diagnose as there is no set pattern to when they occur and as mentioned, they seem to correct themselves relatively quickly.

It started with the E:80 error and this morning, there was an E:74 error for the first time.

Any assistance, guidance and ideas would be very much appreciated! Thank you!

[Markjosephp]

Hello bchambers,

Welcome to the Google Nest Community, and I'm glad you reached out for assistance with your Nest Thermostat. Dealing with intermittent reports like E80 and E74 indicates power issues. While they can be sporadic and self-correcting, it's still important to address them to ensure your thermostat operates smoothly. 

To isolate:

• What type of system do you have? (heat pump or conventional type)
• When did you install it, and when did the issue initially start?
• Did you turn off the power to your HVAC system?
• Do you have a photo of your old thermostat? Make sure your Nest Thermostat is wired correctly and verify that the display is receiving power.
  • You can share with us a photo of your old thermostat and Nest Thermostat's wiring setup.
• Does it have a C wire installed?
• Did your utility company install a box on your HVAC system that turns the system off during high demand (peak) times to save energy? 
• When was the last time you changed your air filter?
• Gather the power readouts in your thermostat's Technical Info settings and inspect for any reports in the Equipment settings.

I'll look forward to your response.

Best regards,
Mark