Nest Thermostat 3rd gen A/C fan will not turn off

[LA-805]

Installed the Nest thermostat 3rd gen almost 2 years ago and it's been working perfectly.  Now the fan will not turn off.  Doesn't matter if AC/Heat or Cooling is on or off.  Turn the system off fan still going, take face plate off and the fan still runs, Only way it turns off is at the breaker.  The fan has been running 24/7 for about 2 days now.  Any ideas as to what could be causing the issue?  Was there an update that was automatically rolled out?

[jenniffert]

Hi LA-805,

Thanks for reaching out here in the community! I'm sorry to hear that your Nest Learning Thermostat 3rd Gen is unable to deactivate your A/C system, regardless of whether it's in heat or cool mode. I understand how inconvenient it is to have to remove the backplate or turn off the breaker to stop it, especially since it's been running continuously 24/7 for two days. Help's here!

To better investigate, I'd like to ask the following:

• Do you have a conventional or heat pump system?
• Have you received any error messages?
• When was the last maintenance and cleaning service performed on your HVAC system?
• Have there been any recent changes or upgrades to your HVAC system?

In the meantime, I’d suggest the following steps:

• Check the Energy History to see if some features are causing the unusual thermostat activation. For more information, see this article: Thermostat Energy History.
• Check that the wires are fully inserted into the terminal and the connector buttons are securely pushed down. This ensures proper wire connections. Important: Before touching any wires, turn off the power to your HVAC system at the breaker box. For reference and more troubleshooting tips, you can check out this article: Troubleshoot strange heating or cooling behavior.

Please keep me posted.

Best regards,

Jenniffer