Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Disconnect rectification lead from the PCB and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance.
Does the burner now ignite or does the fault code still appear?
Note:
As lead is disconnected if the burner ignites, the boiler
will continue sparking then go to lockout.