First, make sure your thermostat is well-powered.
Have you changed the Wi-Fi password of your Wi-Fi router or installed a Wi-Fi repeater? If so, you must reconfigure your installation's Wi-Fi, go to settings in the Home + Control App, select ;Manage my home ;, select the room in which the thermostat is installed, select the thermostat and select ;Wi-Fi set-up ;. Then follow the instructions step by step given by the application.