Hello stuy71,
Thanks for reaching out to the Nest Community. I'm sorry to hear that your thermostat is showing the error E-74. Let's work together for a solution.
To give you the most accurate assistance, could you please provide photos of your current Nest Thermostat wiring? This will allow us to compare and identify any potential issues.
You should find a camera icon or "Insert photos" option to attach the images. If you don't see this on your mobile device, please try using a different browser or a computer.
We look forward to your response and the photos.
Regards,
Kevin
