Drywall boards mold?

Unfortunately, I cannot provide an answer to that, I can only say what is stated in the protocol, possibly they do not go that high

I would be surprised if your heating should run at 55 degrees flow temperature at design temperature - the screed will not thank you

It is about drying the screed. It is common to heat up to 55 °C. Apparently, this is the only way to achieve the required residual moisture for readiness for covering.

Nonsense, the heating-up is done as a stress test for the screed - the covering readiness heating comes afterwards and is normal heating. His values refer to the former. One takes the highest flow temperature that can occur. And nowadays that is very rarely still 55 degrees - and at that temperature the screed will definitely crack. It will be patched again, but unnecessarily.

I'll best call the heating engineer today and ask if he knows what he's doing, but don't the screed layers usually get the protocol?

Nonsense, the heating up is done as a stress test for the screed - the coverage readiness heating comes afterwards and is normal heating. His values refer to the former.

Do you know more than what has been posted here in the thread? I think the description from oggear51 fits very well with the coverage readiness heating.

The screed has now been in for about 3 weeks (cement screed)

Heating was started up today, the first 3 days now with 20 degrees flow temperature and then up to 55 degrees in steps of 5

Matches the description in "Cement Data Sheet; Concrete Technology; B 19 7.2015: Cement Screed". Quote:

The heating is usually put into operation only three weeks after the screed is installed. [...] The flow temperature should be increased daily by max. 10 K (turn off night setback!) starting at +25 °C, until the max. flow temperature of 55 °C is finally reached. This temperature is maintained constantly until coverage readiness. Afterwards, the temperature is reduced in steps of 10 K.

I don't remember anymore, but if the screed has been in for 21 days, no covering-ready heating is carried out, but functional heating - and that is exactly what was described here.

And your information sheet is nice, but with functional heating you go up to the maximum supply temperature - and nowadays that is normally between 35-45 degrees and not 55 degrees. Any good screed layer will always be happy with modern heating systems if the screed only gets its 35-40 degrees.

In addition, the maximum temperature is certainly not maintained until covering readiness, but (I'm writing from memory) for a maximum of 2 days. So...