How complicated are heat pumps in practical operation?

The installation of a heating buffer is being refused.

Every room has the same temperature (+-2°). That’s how it is and how it will remain.

How does the lack of a storage tank then affect extensive use of the shower + bathtub?

Is the fluctuation between the rooms really +-2°C? That is already noticeable at the edge of the personal comfort range.

I have very often read the recommendation to simply open individual controllers fully. If that is so clear, why are they apparently installed that way as standard?

Demand of the KFW. Nothing more.

How does a missing storage tank affect extensive use of shower + bathtub?

You have to differentiate between heating storage tank and hot water storage tank. You usually do not need the heating storage tank, but you do need the hot water storage tank. The statement referred to the heating storage tank.

How does a missing storage tank affect the extensive use of shower + bathtub?

Is the fluctuation between rooms really +-2°C? That is already quite noticeable at the edge of the personal comfort zone.

I am talking about the heating buffer. A storage tank (or a fresh water station) for the domestic water is of course still required.

And the rooms do not fluctuate, but you can, within a narrow range, permanently keep individual rooms colder than others.

why are they then apparently installed as standard?

As already mentioned, KfW and because "we have always done it that way"(c) and well, also because as the installer of the system you often want to avoid problems and don’t want to have to explain to the new homeowner that these things are pointless and it works perfectly fine without them. Because very few home builders are familiar with surface heating systems, and instead of spending hours explaining something, they install the "known" controllers and the customer is satisfied. If then someone comes along who knows about it, even better, then you simply leave those parts out and move on to the next job faster.

Demand of the KfW. Nothing more.

Thanks. So again a senseless condition.

Because very few house builders are familiar with underfloor heating and before explaining something for hours, they install the "known" controllers and the customer is satisfied.

Understandable and very unfortunate.