Hey Markus,
I am currently in the process of switching everything over to a Homie/MQTT based architecture. I was just developing some code today. I guess by Monday I should have something to at least read the values and provide it to MQTT.
I think you could use the 2/Operation/Powerful feature to produce hot-water on demand, but I am not sure if there is a smarter/better way of doing that.
I will let you know when I have some public code.
Karsten