Hi,
I recently integrated my Stiebel Eltron WPF 07 cool via ESP-Home and an MCP 2515 CAN-Bus device.
Total costs around € 30,-- which is nothing compared to the ISG Web device that uses the same bus.
There is some documentation in the web and I share my setup here for anyone who is interested.
It is also possible to actively change settings with the correct bus-commands, but I’m just doing logging of the most important power consumption data.
I’m willing to explain all I found out so far, if there are clear questions.