Our Nest 3G Learning thermostat worked fine, and then we started having strange issues: flashing green light, battery run down, etc. Could not figure out what was wrong. It worked, sort of, but not consistently. Got very frustrated with the Nest!
Here's what happened: During an annual service visit a few weeks prior to check the furnace, the tech replaced the main circuit board on the furnace. The Nest wiring connects to the furnace via screw terminals on the board, so he had to transfer the wires to the new board. He got the colors mixed up, and this was causing the erratic operation of the Nest thermostat! Duh!
Lesson learned: Don't be too quick to blame Nest if it starts to behave badly. Check and double check the thermostat wiring at the furnace if there's any chance that something might have changed!
