I have an issue where the C-wire kept dropping off. When I originally installed the thermostat, all wiring appeared to be fine. But after a day, an error E261 appeared which was low power on the C-wire. So I pulled out the face cover of the thermostat thinking maybe the connection was not tight, I checked the voltage of the red and black wires and there was always 2.7+ volts. When I pushed it back in again, everything was running normal again. In the meantime my battery ran out every 2 days. After a few mishaps like that, I requested a replacement from Amazon for a new unit. What I found was the new nest thermostat was even worse. In less than 24 hrs I got a notice of low battery and the same N261 error appeared.
So I called Nest Customer Service who asked me to read the power etc. A day later, I have exactly the same problem I had with my 1st nest thermostat. I was wondering if I have a bad unit replaced by another bad unit because the C-wire has power.
I am posting the pictures of the wiring of the old thermostat and new Nest thermostat. In the picture, the C-wire is black. The blue wire is a spare wire and was never used. I am still looking for the solution before returning them back to Amazon.
