Replacing floor heating with underfloor heating - is it sensible?

Thank you very much for the great answer!!

The boiler is relatively new, built in 2016, so I assume it is already optimal here.

Do I understand correctly that the existing pipes can possibly also be used as underfloor heating?
That would be even better!

Since the house has received a subsequent cavity insulation, it might be possible to achieve sufficient heating performance.

What does "5-10k" mean and what is a TGA planner?

TGA stands for Technical Building Equipment. The planner can calculate for you how much heating output you have and how much you need.

If the return flow is installed in the floor, can you even mill into the screed?

Okay, thank you.

I don't know if that's possible, but according to the offers, no one has expressed any concerns so far, and no one has suggested to me that the heating can be converted into underfloor heating. But the conversion would only be advantageous for me, not for the respective company.