Firstly, check that the device (smartphone/tablet) with which you want to connect the thermostat is connected to the Wi-Fi network and has a good range to the Wi-Fi network. Also check that the Wifi password you enter in the app is the correct one. (The app will not display an error message if you enter the password incorrectly). The thermostat cannot connect to the network if your network has a 5Ghz frequency switched on. If this is the case, you can log into your network's modem and (temporarily) switch off the 5Ghz frequency. Normally, the connection will then be successfully established. Once the connection between the controller and the device is successful, you can switch the 5Ghz frequency back on in the modem.