How complicated are heat pumps in practical operation?

A lemur is also almost a cat :p

In an emergency, you can follow the recommendation – but by that point, thousands of euros have already been thrown out the window. So it's rather stupid. It's standard because it has become mandatory for some energy-saving regulation classifications. Lobbying would be assumed to be the main reason. Perhaps a bit of backwardness as well. It wasn’t quite so stupid not to heat in the past.

The reason is that the heat pump used to shut off when the ERR throttled the flow upon reaching the target room temperature. This causes the heat pump not to run continuously and to have more frequent downtime. That, in turn, relieves the power grid. And that is exactly the goal. At the same time, your heat pump starts more frequently, which in turn affects the lifespan of the machine (at least with an abnormally high number of starts).

The be-all and end-all is the design of the underfloor heating system and the sizing of the heat pump according to the heating load! Everything else is fine-tuning of the system... Unfortunately, the HVAC technician neither feels like calculating nor discussing with the builder. That’s why he does it the way he always has and pushes 45°C water through the pipes...

That in turn relieves the power grid.

And that in turn is wrong. A continuous, small load is much better for the power grid than many short but high loads. And due to the higher efficiency, overall less electricity is needed, which also cannot be that bad.

It's as if you were claiming that a constantly switched-on light puts less strain on the grid than one that is occasionally turned off. What does efficiency have to do with that?

It's like saying that a constantly switched-on lighting puts less strain on the grid than one that is switched off from time to time. What does efficiency have to do with it?

That's exactly right. Transients strain the power grid far more than a constantly high base load. Study the basics. With the same average power, the on-off heat pump is much more stressful for the grid than the one running constantly at a low power. Provided the on and off signals are not given by grid control for short-term load management. That will come as well.

That will still come.

That has long been common practice with heat pump tariffs?! That's why my heat pump is connected to the house meter! ;-)