Although the post is old, the problem is still open. In my case, the command to set control point is the only way to command the water temperature, hence to control the heather. Unfortunately there is not such device in Domoticz, but I find a workaround in opentherm monitor, that is by using mqtt ...

Same problem for me, I have a Calenta 35. That is very bad because if lower it you cannot increase the water temperature and heat properly your home. Even worse, you can see but not control by acting on the Calenta menu. After many attempt, I have found the solution: I switch off the heater by my on ...