I did find myself a Torx today and took the base of the off. And what do you know, the adjustment ring on the pressurestat is glued on as I suspected (the white blob shown by the red arrow).
Thomas, I thanks for the tips. I'll try and take the pressurestat off and get as much of the glue off before applying any pressure. I have to agree regarding the construction of the Pavoni - it looks like they are cutting too many corners to save costs - the all plastic boiler cap vs the brass threads on the older ones, the plastic p-stat vs the older more solid ones I've seen pictures of, the thin gauge metal on the base vs the thicker one on the old Pavonis etc.
David, I noted your project earlier. Very interesting, thanks. However, I think I'll stick to the fully manual approach of the Pavoni without external components. It might be interesting to try an alternative, higher quality p-stat, though...