Typical plumbers here thinking they know everything, parts are not always needed, always try the simple things before jumping in at the deep end, start from A and work to Z, This is why im a young engineer working for a company who Specialises in compaction repairs and has worked on hundreds of biasi boilers. No I will not be joining this combustion chamber group as I joined this forum to share advice and ask for advice when needed but my first comment gets slated :L forget it il go back to charging for my knowledge.
believe me you may think you know everything about this boiler but I bet you would learn something ( in combustion chamber ), theres probably people in there who been doing it 3 times longer than you was a dribble in your dads pants . we don't mean any disrespect because its just banter but guarantee you will be surprised how much you don't know not how much you do know , but you got to remember the forum rules regarding gas information and if you say what you do is true then i expect you would of come across plenty of situations where this has become evident and caused a dangerous situation for anyone living within that household .