Mine too! I am away and our friend went in to check the house and Nest Thermostat is dark with only red blinking light. Combi boiler and Nest were put in 2 1/2 years ago. I had combi boiler serviced just before we left. When we try to connect from our phone, it says "Off line We had him reboot our router, no change. No one ever said anything about batteries and why, as it is wired in, somehow.
