If the ThermoSmart is offline you can see that by:
The owl at the top left on the portal. If the owl has a sad face, you are not online.
The status LED flashes white on the ThermoSmart if it is offline.
To make certain you are online, first refresh your browser (F5 on a PC, CMD+R on Mac). The owl then has a happy face. If the owl is still happy after thirty seconds, you are online.
If not, first check the Wi-Fi connection.