It could be a number of things, this is not the kind of appliance you should be trying to fix yourself, its complicated & it could kill you. Get a qualified gas engineer round to have a look. It you don't know anyone suitable then call BG or the manufacturer either should beable to give you a fixed price repaire reguardless of how many visits.
I went to one of these the other week where the inner casing had burn through and it was leaking CO into the house (it was the second time this fault had occured) Ferroli are awful boilers, when it gives up the ghost replace it with something German.
Nev, February 2011
