One of three Nest thermostats were successfully attached to my Home account on showed in the app. One of them appeared to be "offline", although it was still connected to the network. I ended up resetting the Nest but it now will not connect to the Home account via the Nest app. I have tried using the UPC code and also the entry codes.
The Nest thermostat is connected to the same wifi network and is otherwise working, but fails to connect to the account via the app.
Thanks for posting and sorry for the delayed response. I want to check on your thermostat why you're unable to add it to your Nest app.
A few questions — are you getting a specific message or a code? If yes, what is it? Also, what is the make and model of the mobile device that you're using? It would be great as well if you could provide a rundown of the steps you've tried so we can pick up from there.