floor heating: constant floor temperature independent of indoor temperature

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I am already used to the phenomenon of low radiant constant flow systems. But this system works on the basis of "constant vol Rad Htg Hi air temp", in other words indoor temperature.

I want the floor heating to always be on at 40 ° C so that the floor temperature becomes constant 21 ° C. Regardless of the room temperature. How do I do that?

I only use floor heating as heating and in winter.

Isn't this the right way how floor heating works?