dennis@home brought next idea :
IIRC one of the add on controllers allows for different temps when running HW
and heating but I don't recall which.

It would have to be something which interacted directly with the boiler
and Vailant said there was nothing able to do that, when I spoke to
them. The boiler has the built in interfaces for the fancier control
systems, I understand, but little detail to be found about these extra
systems.