Since Events2HVAC communicates directly to the thermostat using it’s IP address and ASCII port, you want to make sure you are using a STATIC IP address. In the web UI of the thermostat, go to the “Configuration” tab and select the “Network Settings” button.
Uncheck the “Enable DHCP” and enter a static IP address in the IP Address field. You can optionally choose to check “Enable Login” to force any user to login before using the ASCII API port.