Air-water heat pump combined with underfloor heating does not work properly

That means where I have defined or set my maximum heat per room after the thermal balancing, I turn the temperature controller to max. Unless I want a room to be a bit cooler, then I turn the temperature down. Is that correct?

Honestly, I also find it an imposition what has been imposed on us as builders. I want to make my life easier, not more complicated.

Yes, you can see it that way or not. Compare it to computers or the internet / modern devices where nowadays you almost can’t get by without registering online or via an app. Not everyone can do that from birth either. Our world is becoming more technical, which requires certain knowledge or training, or you pay someone for it.
The problem right now is that those who install the heat pump often don’t have enough knowledge/experience themselves and have too much work, so the heating engineer then happily says, yeah, I set it roughly, the rest can be controlled by the thermostat (yeah, sure).

Please look up thermal balancing separately in a search engine.
The principle is that you open everything fully. (It should then become too warm almost everywhere; if it gets too warm everywhere, then you could also lower the flow temperature, etc.) And then slowly start turning each one down individually until the appropriate temperatures prevail in the rooms. (also very simplified) Since the system is sluggish, you have to wait one day after each change to see the effects. Also, sunlight or similar can still influence the result.

But if you have done it correctly and the system is not otherwise messed up, you can leave the room controllers fully open or even unscrew the actuators.

So, if you set the thermostat to 18 and the room gets warmer, it will not heat there.

Completely independent of whether gas, air-to-water heat pump, etc.

It gets warm there due to other influences: sunlight, adjacent rooms, people, etc.
That's where you can start.

Edit: of course, you can check if the thermostat is working properly!

Yes, you can see it that way or not. Compare it with computers or the Internet / modern devices where nowadays you can hardly manage without registering online or via app. Not everyone is born knowing how to do that. Our world is becoming more technical, which requires certain knowledge or training, or you pay someone for it. The problem currently is that those installing the heat pump often do not have enough knowledge/experience themselves and have too much work, so the heating engineer then likes to say, yeah, I roughly set it up, the rest can be controlled at the thermostat (sure).

Please look up thermal balancing separately in a search engine. The principle is that you turn everything up fully. (It should then get almost too warm everywhere, if it gets too warm everywhere, then you could also lower the flow temperature, etc.) And then start slowly turning down each individually until the appropriate temperatures prevail in the rooms. (also very simplified) Since the system is slow, you have to wait one day each time before you can notice the changes. In addition, sunlight or similar can still affect the result.

But if you have done it properly and the system is not messed up otherwise, you can leave the room controllers fully turned up or even unscrew the actuators.

That’s correct. It just keeps increasing and that makes you more and more annoyed. And I say this really as someone interested in technology.

Your simplified explanation of thermal balancing is exactly what needs to be done. That’s how I understood it from my research.

So, if you set the thermostat to 18 and it gets warmer in the room, it won’t heat there.

Completely independent whether gas, air-water heat pump, etc.

It gets warm there due to other influences: sunlight, adjacent rooms, people, etc.
That’s where you can start.

Edit: of course, you can check whether the thermostat is working properly!

Regarding the sun, I can darken the room using the blinds. I can only partially influence adjacent rooms.

You do not make the basic setting! not via the room thermostats but via the balancing of the volume flow at the HKV. Read up thoroughly on the topic of hydraulic and thermal balancing again.

You do not make the basic setting! not via the room thermostats but via the balancing of the volume flow at the HKV. Read up thoroughly again on the topic of hydraulic and thermal balancing.

I have already understood that it is controlled via the volume flow.

Good. Then you only need info on how the individual rooms are equipped with the underfloor heating.