I Installed the Nest thermostat for heating, during the summer, with 2 wires (R and W). For months, the display worked properly when I walked by, I could read the room temperature, etc. This week, the thermo attepmted to use the heat for the first time. History log shows that the heat came on for 10 seconds. Now it displays no power. The setup diagnostics on the thermostat show that no wires are connected. Update, now it shows a white wire connected.
I have tried: Installing a Nest Power Connector. Resetting the thermostat. Taking the thermostat to the heater room. Removing the Power Connector and setting it up from scratch with a C wire. Replacing the batteries.
After resetting the thermostat, I can no longer get through setup. It shows only the W wire is detected. C wire not detected and R is empty. Even when the R, W and C are short wires coming directly from the heater panel itself.
Using a meter, I can see it's sending around 24V ac to the C wire connection.
Could it be that the thermostat is damaged?
Found my answer. My boiler is so old it doesn't have anything like a C wire. It took me a while to discover that the C wire is NOT power, It is the return or neutral wire from the same 24v ac source. Many posts discuss the need for a C wire to get consistent power, but that's not the C wire. The Red wire(s) provide power. And the C wire is the complement of the power, a neutral wire coming from the same source. Knowing that I could connect the C lead for the Nest Power Connector correctly. I'm to the races. (google instructions don't provide under the hood information),
I'm happy to see that you got this sorted out and I appreciate you sharing here how you got things fixed. Before I mark this as resolved for you I wanted to check in and see if there was anything else you might need on this. If you have any other needs, just let me know.
Even after the above change, things still failed when the heat kicked on. My final fix was to follow the Nest power connector pro installation guide, found through some other posts. After adding a compatible 24v wall adapter in my boiler room, connected to the power connector per the instructions, I finally got heat all through the night.
That's definitely good news, klojewski. Are you feeling like it's all set for now? We can watch it for a few days to ensure it stays working as intended. Let us know if you see any changes.