How often is it normal to fill the heating circuit in a new building with underfloor heating?

5 people have written that it is not normal to have to refill a FB heating system so often and so much. What would you like to read? If your heating engineer says everything is fine, that's great. I find it strange.

Heating circuit - is after all a closed loop - just think about it yourself

Best option would be a broken or undersized expansion vessel.

Worst would be a defect in the [Fußbodenheizung System].

Middle option would be a leaking safety valve.

As a plumber, I would also claim that everything is okay if it would become expensive to locate and fix the leak.

Such a massive pressure drop is not normal in my opinion. We used to have something like that in the gravity heating system when the open expansion tank in the attic had eventually evaporated empty.

The expansion vessel in the device has an autovalve and pressure probably escapes through it, and with a capacity of 12 liters, you probably notice every ml of loss. The vessel is tight as far as I can judge myself. Otherwise, everything in the boiler is dry and tight.

The self-venting valve was slightly open, maybe some was lost there as well.

I have now refilled about 500-1000ml and increased the pressure from 0.8 to 1.8 bar.