fan flue faults are generally air pressure switch faults or a blockage on associated connections.
typical aps fault would be when you demand hw for example you'll see the demand light come on, hear the fan spin but no ignition clicking then the fault led will flash.
basically the aps is a safety switch which proves the fan is running and if something is blocked or switch is hitty missy then it thinks the fan has failed so will not ignite the boiler.
dont get involved with money, just do the work get a wage but if you guess allowed £20 for aps and hour labour.
you may also get a call out charge first as my advice is based on your description not actual life experience.
but 90% on fan flue faults are aps, blocked venturi, brittle hoses.
iain
October 2008