Central room temperature controller for ERR underfloor heating

Yes, you have a misconception.

..

The only place where the temperature should be regulated, after successful thermal balancing, is the heating curve of the heat pump.

Since the ERR prescribed by the Energy Regulation is mandatory, it is also installed by the main contractor. That means, according to the regulation, controllers/sensors must be in every room!

I can also perform the thermal balancing with wireless thermostats (or just deactivate them and do it manually) and then deactivate\decouple them

@ Alessandro
You adjust the flow at the distribution box of the underfloor heating once for each room so that this room reaches its normal setpoint temperature.

At that time, look up thermal balancing to understand the process exactly.

Assuming your setpoint temperature is 21 degrees as in your example.
The room now also has 21 degrees.

Then, simply put, the following happens:
The heating water arrives at the appropriate supply temperature, since the room already has 21 degrees the heating water can no longer transfer heat to the room and flows out again at the same temperature.
The water returns to the heat pump having lost almost no temperature.
Now the water can either go to another room and be used there, or the heat pump detects that no consumption takes place and reduces the output.
The goal with a heat pump is always to run it as long as possible at the lowest possible output.

If you now regulate this via thermostats, the following happens simply:
Heating water runs, thermostat regulates down,
The flow rate is significantly reduced since at least one room is missing.

Here it can already happen that the heat pump goes into fault mode because the minimum flow rate is not reached.

Heat pump switches off because no heat is being drawn.
Thermostat notices the room temperature drops and releases supply, heat pump starts up at full capacity, runs 2-3 minutes and is then throttled again by the thermostat.

And now you have a heat pump that has to make dozens of starts per day, and wears out faster.

The best control is always the internal one of the heat pump or the condensing boiler.

Thank you for the explanation!

As a reference, here is also an older post from you:

edit: asked, how could I deactivate the ERR?

Yes, Err must be installed if you do not have an exemption, but you do not have to use them. Unscrew actuators, adjust flow once and then operate via heating curve.

That all makes sense to me. However, especially during the transition period, I often have different temperatures due to foreign entries in the rooms, which causes unnecessary energy waste at low outdoor temperatures because the heat pump provides too high flow temperatures.
This regularly happens particularly in modern new buildings with very large window surfaces.

I do not understand your explanation that the heat pump goes into fault mode if the minimum flow rate is not reached.
According to that, this would also happen if the heat pump only heats the domestic hot water in summer or if the 3-way valve closes the entire heating circuit.
It would make little sense to require an ERR where the heat pump regularly goes into fault mode due to the minimum flow rate not being reached, for example, because all bedrooms do not demand heat and the heating circuit valves are closed.
The heat pump also does not start at full capacity when there is a 0.5°C delta-T from the room thermostat.

Permanent flow through open valves also means that the pump can never operate at lower power.

Of course, an ERR in a underfloor heating system never has the advantages that it has with radiators or air conditioning systems, but it still (especially during the transition period with large outdoor temperature fluctuations) has its justification.

That is why the manufacturers prescribe buffer tanks for most heat pumps. Have you tried adjusting the heating curve during the transition period? That often helps. Pumps are nowadays automatically controlled anyway, and the flow rate should be appropriately designed for the heat pump. For the domestic hot water, the heat pump usually has a high flow rate.