Daikin Altherma 3 and termostats

Hi! I have a question if anybody has a clue about this situation?

We have Altherma EHVX04S23E6V and 7 room thermostats. Underfloor heating is linked with Altherma and gives a signal when thermostats reach the temperature, so pump stops working.

I have experimented with weather dependent curve, it was working, but in times when the temperature outside rose from 1C to 14C, the house overheated. It is a very well-insulated new house. Underfloor heating has electrical valves (sorry if the term is not adequate, non native speaker here :)).

So I switched from weather dependant to fixed flow with regulation with an external room thermostat.

The thing that is happening is - I've set the main zone to 31 C. And Altherma at some points during the day (points which I haven't figured out yet) drops the main zone temperature to 27 C.

I would have assumed that thermostats have reached room temperature, but that is not the case.

And then I would wake up in the morning and have a "chilly" room.

Most of the thermostats are set to 23C but this temperature is almost never reached (outside is 4C). Ok, maybe I need to raise the main zone to 32 C, and have Zhender recuperation on (low speed) all day, but this just bugs me. Why is Altherma deciding alone to lower the main zone if I have set it to 31C?

And interesting also is that you can't make a schedule for the main zone if you control Altherma with thermostats (that by the way have no option for scheduling...)

If anybody had this kind of problem, help would be appreciated.

Our service guys are useless...they said for eg. weather dependent curve is BS :\

Thank you!