The most common reason for the mobile application not working is related to your WIFI signal strength.
The mobile application relies on your Altistat™ Controller's ability to connect to your local internet in your home. If you are unable to access your mobile app, the issue is likely related to the connectivity and/or signal strength in your home. To trouble shoot, please touch the gear icon on the top right of your Altistat™ Controller in your home. Then navigate to the Network tab. Once there, ensure that you are connected to your local WIFI network. If you are connected and you are experiencing intermittent service with the mobile application, consider adding a WIFI repeater to boost the signal strength in your home.
Also, if you have a network firewall, Altistat™ will need the following ports open: 443, 8883, & 8443.