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E74 error, but Rh has 28 volts

GoldMember
Community Member

‎07-27-2024 04:22 PM

Hi. I've had my nest thermostat for many years and it's worked well. Suddenly, last night it showed offline on the app. The app tells me there's no power to the RH wire. I pull the thermostat face and check the power to the RH wire between RH and C and get 28 volts on my multimeter. Yet it still tells me no power detected on RH. I have another of the same nest thermostat in the house. I put the face on the same base and it reads the same, no power to RH. What could cause this?

Battery 3.6v

Voc/Vin/lin: n/a

Thank you!

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ovidioj
Community Specialist
Community Specialist

‎07-30-2024 05:46 PM - edited ‎07-30-2024 05:48 PM

Hello @GoldMember,

 

Thank you for posting in the community. 
I understand the frustration you're experiencing with your Nest thermostat not detecting power on the RH wire despite having a consistent voltage reading. I appreciate your effort in providing information.

To help me troubleshoot this issue effectively, please provide the following information:

  • Thermostat Model: Please specify your Nest thermostat's exact model.
  • HVAC System Type: Is it a forced air system, heat pump, or other type?
  • Wiring Configuration: Can you describe the wiring setup at the thermostat base (e.g., C, R, W, G, Y, O/B)?

While I gather more information, you can try the following steps:

  1. Remove your thermostat from the base by gently gripping the thermostat ring and pulling it toward you, away from the wall. The thermostat display should pop right off the base.
    Charge your thermostat with a USB cable for at least 10 minutes. Newer Nest thermostats use micro USB, the same type of charger as many cell phones, cameras, and other electronics.
    After your thermostat charges, reattach the display to the base. This should give your thermostat enough power to turn on and show you a message that can help you troubleshoot.
  2. Check the air filter.
    It’s important for your system to have good airflow to run properly. A clogged air filter in the summer can limit how much air flows over your cooling coils. If this persists, your cooling coils can freeze solid and cause your system to shut off.

Please follow the steps above; if they did not work, please click on this link: Troubleshoot thermostat power issues (E74 error) to troubleshoot the issue. 

Let me know how it goes. Thank you. 

 

Regards, 
Jorge

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