Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect the ignition lead from the PCB and remove the electrode assembly from the main burner
Disconnect the ignition lead from the PCB and remove the electrode assembly from the main burner
Measurement:
Check the continuity and condition of the ignition lead and electrode assembly.
Isolate as per TOPs P4
and refit as necessary