Google Nest Community

Or you might have a bad wire? Have you reinstalled your old thermostat to see if it works properly?

All 4 of the thermostats were new. 2 Nest, 1 smart Honeywell and a very basic non smart one. Fan ran with all of them. You will know for sure its not the thermostats or the wiring at the thermostat. If you turn off the power at circuit breaker to you...

Disconnecting G wire did not work for me. Subsequently, I installed/uninstalled 3 different thermostats. I suspected it was the fan relay switch. It was. I called an HVAC guy. Inexpensive part but expensive labor.

I have a c wire and fan still runs constantly