Heating phase, screed, window position

Do you mean that 60 degrees must also be reached during the functional heating when the heating will only reach a maximum of 35 degrees in operation?
I have always read otherwise. DIN1264-4 also says raising to design temperature for 4 days.

There are two answers to your question:
1 (formally correct): Heating up to 60 degrees is mandatory, as only then the warranty applies.
2 (reasonable/practical): Heating up to 60 degrees is nonsense for underfloor heating designed for max. 30-35 degrees.

If the surface readiness heating as well as the preceding functional heating are not operated with the maximum possible flow temperature, the surface readiness of the screed can also be achieved, but due to the greater screed thickness between the heating elements, it will not be reached within the required timeframe.
This means: when laying the floor covering, the screed does not have the necessary dryness in cross-section.

That is correct, but not disastrous. Then heating will take longer and every floor layer will measure the moisture of the screed. Therefore – with a decent craftsman – the risk is zero.

If the specifications that represent the current state of the art as well as the rules of the trade are deviated from, the risk that the screed will be damaged is very high.

The problem is that these rules still do not include underfloor heating with 30-degree flow temperature but generalize.

Conclusion: for functional heating and surface readiness heating, you must reach the 60 degrees for the warranty, unless the screed layer guarantees it at lower temperatures. Otherwise, you have no practical disadvantages, since the function of the screed is tested at max. flow temperature (+5 degrees).

I have to strongly disagree with that serious problems will occur if you do not reach 60 degrees. Literature increasingly also speaks of "up to 55 degrees or the intended maximum flow/design temperature." Thus, there is a growing realization that it also makes sense to deviate from regulations. It changes from "maximum possible flow temperature" to "intended max. flow temperature."

The purpose of the whole thing is, on the one hand, to determine (during functional heating) whether all components in the installed heating system are working correctly.

In heat pumps (unfortunately) rarely the case. Many heating installers do functional heating with Hotboy and co. The heat pump as an important part of the heating system comes later. Therefore, in practice, functional heating is probably more about the screed than the overall system.

That means: when laying the floor covering, the screed does not have the necessary dryness across the cross-section.

With us, measurements are taken between the heating loops. The distance is maximum due to the central drilling. Whether it was dried ready for covering at 35 or 60 degrees makes no difference. Dry is dry and wet is wet. That can be measured.

I hope I was able to explain that understandably.

For me, it jumps too much between functional and covering readiness heating. And no concrete figures. In the standards and on the internet you can find everything between max flow temperature and 65 degrees. So far, I have not seen any meaningful reason why one should go significantly above the max design temperature during functional heating.

There are two answers to your question: 1 (formally correct): Heating up to 60 degrees is necessary, as only then warranty applies. 2 (sensible/realistic): Heating up to 60 degrees is nonsense for a floor heating system designed for max 30-35 degrees.

Thanks for clarifying that again. So the recommendation is to talk to the screed installer and explain it to him. But that doesn’t seem to be so easy. ;)

and For clarification: The P7 protocol for the proof heating of screed (Federal Association of Surface Heating and Surface Cooling e.V.) already states that it is not necessary to heat at full power all the time, but only up to the maximum design flow temperature. Not up to the maximum possible temperature. During functional heating per se, only the maximum design temperature – i.e. 30-35 degrees for the heat pump.