Don't know if it helps but we have some Ferroli boilers about 1992 vintage. One fan was vibrating, which then set up very loud vibrations in the cabinet. Those fans are centrifugal fans, which have an impeller which ideally is very light, especially at the circumference. So check that the fan spins smoothly (disconnect all power first of course). If so then check that the blade does not spin eccentrically, and maybe bend it a little if it does. And of couse there should be no obvious damage. But the secret, which I found with mine is that after some years there will be a build up of dirt on the blades, just where you don't want a buildup. So give the blades a good, gentle cleaning. Hope that helps.
Brendan, May 2009
