Try adjusting the temperature with your thermostat to stay comfortable while you troubleshoot.Follow the troubleshooting steps in this article.You'll be able to control your system with the thermostat, but not with the app.Follow the steps in Troubleshooting when your thermostat won’t turn on.
Follow these steps if your Nest thermostat has been previously connected to your Wi-Fi network but disconnects repeatedly, or if it's offline in the Nest app or on the thermostat display.