Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Measurement:
Disconnect the Burner Flame Sense
Electrode Lead from the Sense Electrode.
Measure the Lead continuity between the
disconnected Lead and connection 8
(Grey wire, marked FLAME P) on the PCB
connector multiplug.
Replace lead.
Electrode Lead from the Sense Electrode.
Measure the Lead continuity between the
disconnected Lead and connection 8
(Grey wire, marked FLAME P) on the PCB
connector multiplug.
Replace lead.
Isolate as per TOPs P4
and refit as necessary