I know there a number of UK fhem users who have MAX! systems so I'm adding this post as a pointer to https://forum.fhem.de/index.php/topic,58927.msg503182.html#msg503182 (https://forum.fhem.de/index.php/topic,58927.msg503182.html#msg503182)
Probably a thread worth following
The first post links to a pdf in English.
Useful info. Shame they didn't do an open therm interface as well as you have much more control with that and some boiler support open therm. On/off control is hardly hi-tech although it is what all boilers will support.