Old post maybe, but deserving of an answer (one at least) for others that are searching about just such a problem. Me for instance, last week.
Emailing Ferroli technical help (twice because I didn't believe them) told me I couldn't replace the integral Auto Air Vent, but would have to buy the whole pump (at £120+), even though the pump was quiet, checked and cleaned of (minimal) rust debris (and whole system thoroughly descaled too a few months earlier).
The AAV in this model (and some others) has a brass knurled screw-on cap, with a logo on it, screwed onto a body moulded into the rear of the Grundfos made pump. After a bit of a search, this turns out to be a Caleffi logo, and the cap/valve/float assembly is from their Minical 5020 series, AAVs from which can cost less than a tenner. 502040 is the 1/2" fitting for instance.
Not everywhere has the Caleffi Minicals. Make sure online merchants aren't going to substitute a 'Robocal' instead, nor a different make with a different thread or body size - without asking nor telling you. Both happened during search. Or support your local plumbers shop where they'll be knowledgeable, and have catalogues.
As a quick aside, cleaning the old AAV didn't work, and disabling its 'auto' mechanism worked only somewhat - turning a leak into only a weep 'til a new one was got.
Drain system to just below pump, unscrew old AAV, screw in new one, fill up system and listen to the new AAV go whoosh then stop abruptly. Plastic cap on it should be loosely on to allow it to work. It can be left loose, or later tightened after all air out of system. Left loose it allows air previously dissolved in the new water to vent as and when it comes out of solution as the heating is used. Simples. And make sure there's enough inhibitor in your system.
Now to write an annoying email reply to Ferroli... who are I suppose only doing their job. Which is selling more Ferroli stuff, not necessarily providing accurate technical help.
Modena generally been an ok boiler for 10 years, but certainly had its probs, a list of which could - but won't! - follow.
Hope the above helps someone.
