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C Wire Issues

Kemberlee
Community Member

‎08-11-2025 04:28 AM

Hello, 

i recently had the Nest Learning 4th generation thermostat installed. It was working fine for 2 days. Now I have Error E448: No system power. When looking into it it's saying no power to the C Wire. All wires have been tested and has power. is the C wire needed? How do i fix this? 

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GabrielaG
Community Specialist
Community Specialist

‎08-14-2025 10:36 AM - edited ‎08-14-2025 10:36 AM

Hi @Kemberlee,

 

Thank you for reaching out to the community. I'm sorry to hear your Nest Learning Thermostat 4th gen is not working as expected and is showing the E448 error code. No system power referring to the C wire. No need to worry; I'm happy to help.

I really appreciate you letting us know you've already tested the wires. That's a helpful first step. To provide the most accurate troubleshooting, could you please provide the following information? 

  • During the installation of your Nest Thermostat, the Google Home app mentioned something about the C wire or offered you the Nest Power Connector?
  • Do you have a spare wire that's not connected anywhere on the HVAC and the thermostat?
  • Do you have a pre-existing thermostat?
  • Could you please send me a picture of your Nest Thermostat wiring?

I look forward to your response so we can find a solution for you soon.

 

Regards,

Gabriela

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