Okay so much more digging around if you haven't solved this. You'll have
to remove the nest from your nest app and re-add it. The nest walks you
through how to do that. Good luck!
I too am having this issue. My phone says "nest is not connected" I
check the nest and it has connectivity to the router and I can see that
the wifi is working. The app is just not seeing the device as on line.
So I can't change temp. Start the fan e...