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After power outage system blows hot air nonstop instead of AC

NestUser37
Community Member

‎08-05-2024 04:43 AM

This has happened to me now twice in two different houses.  We have forced air heating/cooling.  After a power outage, we wake up to find our heat blasting at top volume when our Google nest is set to Cooling mode.  Turning off the thermostat/resetting the temperature does nothing.  We have had to shut off the emergency power to our boiler to make it stop.  The first time we caught it when the house was at 81 degrees, the second time it got up to 101 degrees in the one zone.

First time (house with 1 zone, oil heat): after shutting off boiler, we turned it on again the next day and system seemed to be reset. 

Second time (house with 3 zones, propane heat, new AC condenser): boiler was shut off but fan continued to blow even when thermostat was set to "off" again so I had to shut down the breaker.  We are still troubleshooting as now one of the circuits in the fuse box seems to have blown.

This is NOT a wiring issue: our Nests have been installed and working fine for years.  Now this happened twice this month.  Is there a new software update or bug?

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jenniffert
Community Specialist
Community Specialist

‎08-12-2024 01:38 PM

Hi NestUser37,

 

Thanks for posting in the community! I'm sorry to hear that your Nest thermostat is blowing hot air instead of cooling air. I'd be happy to help.

 

To better assist you, please share a picture of your wiring installation and provide the following information:

 

  • What is the model of your Nest thermostat?
  • Do you have a conventional or heat pump system?
  • Does the inconvenience happen with both heating and cooling, or just cooling?
  • Have you received any error messages?
  • When was the last maintenance and cleaning service performed on your HVAC system?
  • Is this the first time you're using cooling this year? If so, did heating work without issues during the winter?

As you've noticed, a blown circuit is a potential issue. Ensure all breakers and fuses are in good condition. For now, I’d suggest the following steps:

 

  • Check the air filter. Your HVAC system needs good airflow to operate properly. 
  • Verify if the thermostat screen turns blue when you want cooling (or orange for heating) but the HVAC system doesn't turn on.
  • Ensure the wires are fully inserted into the terminal and the connector buttons are securely pushed down. This guarantees proper wire connections. For reference, you can check out this article: Troubleshoot strange heating or cooling behavior. Important: Before touching any wires, turn off the power to your HVAC system at the breaker box. 
  • In case you have the Nest Learning thermostat, please go to Settings > Technical Info > Power on your Nest Learning thermostat and provide me with the VOC, VIN, and IIN values.

Please keep me updated.

 

Best regards,

Jenniffer

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