Stiebel Eltron ISG Modbus interface

ISG (Internet Service Gateway)

The ISG is a device that lets you manage your heat pump using a web portal or a smartphone. It is connected to the heat pump using a CAN bus connection. It has a network port to connect to the local network and use the internet to connect to the Stiebel Eltron Service Portal.

The ISG uses DHCP to obtain an IP address. If no DHCP server is available, the default IP address 192.168.0.126 is used. Ping 'SERVICEWELT' to find the correct IP address or check your router. You can access the web portal using a browser to connect to the IP address or http://servicewelt/ unfortunately only http not https.

ISG Web Portal

Home Automation

This is howerver not the only function of the ISG, it also exposes a Modbus API to control the heat pump. This allows the heat pump to be integrated into a home automation system like Home Assistant and Homey. The Modbus API, is available on TCP/IP port 502. Unfortunately the Modbus API is not enabled on all ISG’s. It seems you need at least version 12.2.2 of the firmware installed on the ISG. If the API is not available on your ISG, you can contact Stiebel to enable the API on your ISG.

Check for Modbus API

Check if the API is available on your ISG by running a telnet command. If the terminal window goes black, it is connected and available:

Telnet

If the API is not available you will see a failed to connect:

Telnet

If the API is available you are ready to use the Homey or Home Assistant to manage your heat pump.

The Modbus API has some shortcomings for retieving power consumption. This is essential information for efficiently managing your heat pump. The community has found ways to fix these shortcomings. Check the links for more information about these changes.

Links