Are some of our developers here aware of open3e project where you can access viessmann heater via USB CAN-Bus adapter and MQTT? Not sure if this is already known here otherwise forget my post.
I found this project in this thread where you can get some more information
https://www.viessmann-community.com/t5/Konnektivitaet/CAN-Bus-Home-Automation-E3-Generation-lokal-und-kostenlos/td-p/356066 (german language).
Link to USB CAN adapter for 35€