hi there have the gas pressure checked by a good and i mean a good engineer if boiler is not going into full burn on high demand the boiler will shut down.
this is a very common cause of boiler failure.
also check it is wired correrctly as the ferroli should have 4 wires to it a permanent live a switched live plus neutral and earth lots of people leave out the permant live again causing boiler to go into lockout as the pump cannot over run to disperse the heat
martyn
July 2006