One of my Nest Learning Thermostats just started flashing a red dot after 5 years of working fine. I can charge it via a USB charger and that works for about 36 hours and then we are back to red dot. I have not recently changed anything in the HVAC system this unit controls. I have another Nest Learning Thermostat that is 6 months older and controls another furnace and AC and it is still running fine. It isn't clear what changed to cause this. The battery does still take a charge via USB, so I don't think it is bad batteries, but clearly the unit is not liking the power it is getting from the wiring we have had for many years and that was working fine. Both thermostats saw new AC units installed 3 years ago and that is the last change we had in this house's HVAC (two independent systems).
Do I need to replace the thermostat every 5 years or so?
