ᐅ How often should the heating circuit be refilled in a new building with underfloor heating?

Hello everyone,
how often nowadays does water need to be refilled in a new building (built in 2016) with underfloor heating?
We have a Viessmann gas boiler and about 140m² (1507 ft²) of heated area.

Currently, I need to refill water about once a year because the pressure drops from 1.5 bar to around 0.9 bar. The underfloor heating only runs about 7.5 of 12 months, and the rest of the time only hot water is produced.

In your experience, is this still within a normal range, or should I start to be concerned?

You have a leak.

Underfloor heating systems are generally maintenance-free and should ideally be left undisturbed. Refilling the system with new water introduces fresh oxygen, which promotes corrosion and sludge buildup.

oh oh oh this is going to be expensive

Your heating system is definitely leaking. If you’re lucky, it’s just a fitting on the manifold that’s not tightened properly. Maybe wipe everything down with a dry cloth after you’ve refilled it. But I guess you would have already noticed that...

My tip... defective expansion tank.

Or there is still air trapped somewhere in the system. In our case, it was in the heat exchanger of the hot water tank, which I hadn’t properly vented.

Other than that, I have only needed to top up the system once in a year, just a little bit (from 1.6 to about 1.8).