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N406 , no power detected on g terminal

Powerfuldodge
Community Member

a month ago

I had the nest 1st gen thermostat and just replaced it with a new gen 4. The 5 wires are in the same terminals but it won’t heat , cool or turn the fan on . I’m getting code n406 and it’s says no power on the G terminal which there shouldn’t be unless the fan is running . I removed all the wires and and jumper Ed each circuit and the heat , cooling and fan work. Just seems like the thermostat does not have any output , on the from it will show fan running but down at the furnace their is no power on the green wire to make the fan turn on . Any suggestions or things to check

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1 REPLY 1

kcruzgonzalez
Community Specialist
Community Specialist

4 weeks ago - last edited 4 weeks ago

Hello @Powerfuldodge,

 

Thank you for posting in the community. I'm sorry to hear that you're having trouble with your new Nest Thermostat Gen 4 getting the error code N406 that indicates no power to the G terminal. Thanks for trying the steps and for confirming that your furnace and wiring are working correctly. Let me help you with this.

It would be very helpful if you could share a few photos with us.

  • A photo of your old thermostat's wiring before you removed it.
  • A photo of your new Nest Thermostat's wiring.
  • Have you already had a chance to check the voltage of your wires?

If you have, we can try running a diagnostic test.

Important: Before you touch any wires, be sure to turn off the power to your HVAC system at the breaker to avoid any damage or injury.

  • Swap the G and Y wires: Carefully remove the G and Y wires from their terminals on the Nest Thermostat and swap them. This means the G wire will go into the Y terminal and the Y wire will go into the G terminal.
  • Check for a new error: Turn the power back on and see if the thermostat displays a different error code or behaves differently. This will help us determine if the issue is with the thermostat's internal wiring or with your system's G wire.
  • Reinstall your old thermostat: Please try reinstalling your old thermostat. This will help us confirm that your HVAC system is still working correctly.

Please share the photos and let me know the results of these tests when you are able. I look forward to hearing from you.

 

Regards,

Kevin

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