for any boiler fault I would always advise contacting the manufacturer helplines first for advise
they are normally quite helpful in pointing you in the right direction as to the possible cause of the fault
they would not ask you to take the boiler apart to perform tests
they would ask to simple things like
''fault indicator light sequences'' or
''can you hear the pump/fan running?'' etc
if they are able to diagnose the fault over the phone & the boiler requires a part then at least you would be in a better position to judge:-
1.cost of new part
2.how much would a gas engineer charge in labour to fit part
you can contact Biasi on 01922 714600 where they will be happy to help
mac
April 2015