I have a 17 month old Baxi solo 3 boiler which started throwing fuses
yesterday. Initially when I realised the heating had gone off I found a
circuit breaker in the CU had tripped, reset this and all was OK. Next day
the same thing happened but once the circuit was reset this time only the
'Boiler On' light on the control panel illuminated, no 'Fan On' light and no
Pilot or Burner lights.

I located the installation manual and identified the circuit board fuse,
this had blown so I replaced it with the spare and once again all worked
normally for an hour or until this time the 3A fuse on the isolation switch
blew (Baxi state this should be 5A?). Once again replacing this worked for
about 20 mins until it blew both the isolation switch 3A and the circuit
board fuse.

Any ideas what may be causing this and where can I source a replacement fuse
for the circuit board which is marked F4AH250V?

TIA