I guess that you refer to the MDT heating actors? I use the same actors and when I remember right, I’ve tried to do in the same way than you with having your troubles as well. My impression was, that the “Sollwert Komfort” communication object is there, but there is not much of a documentation or how to use it.
So I went using the suggested standard way in the documentation and only set the HVAC mode via communication object 10 (Betriebsartvorwahl, DPT HVAC Mode 20.102). I’ve added a heating schedule that will change the HVAC mode throughout the day (Comfort, Standby, Economy, Building Protection).
Also I use the nominal temperature value shift using the communication object 8 (manuelle Sollwertverschiebung) as a 2 byte value if my flatmates feeling too warm or too cold.
To have that nicely packaged within a custom widget, I started here:
And got a lot of examples from other people doing the same.