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

We had to refill our heating system repeatedly. Twice a compensating vessel was defective, and the connection to the water supply was also found to be leaking. At the beginning, we repeatedly had some air in the system. Draining caused pressure loss --> refilling. It doesn’t have to be expensive. Our floor heating boiler and surface-mounted water pipes (radiator connection) in Berlin received additional water once a month and ran dry and reliably. Where the pressure was released - no idea.