New underfloor heating system with heat pump is losing pressure

As far as I have read, a pressure of 1.5-1.8 is okay for our underfloor heating with air-to-water heat pump for the house, but mine has gradually dropped to 1.0 now (however, in a total of 5.5 years of operation). I think that is still okay, right?
Next week someone will come by for inspection (MAG and valves) and maintenance (cleaning, venting, refilling) of the system, then we will see if something is defective or if it just needs to be refilled.