Screed drying with underfloor heating: How is it heated?

The pipes are not pinched but could contract slightly without pressure or might be about a tenth of a nanometer more taut under pressure. And when pouring the screed, there must be pressure on the underfloor heating. Often this is done with air pressure if the heating is not yet installed. This also serves as a leak test to ensure that nothing leaks anywhere in case the underfloor heating has a defect. It could be damaged mechanically or from the factory.