Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance

Measurement:

Inspect all three electrodes (2 spark & 1 rectification) for good overall condition i.e. clean, no cracked ceramic and not warped.
Measure the resistance across each electrode - expect continuity/zero resistance.
Measure the resistance between each electrode and the metal on the electrode bracket (expect 1 MOhm or greater or O.L).
Check the gap between the two ignition electrodes is approximately 4mm.
Note:
Electrode assembly must be refitted with a new gasket on reassembly.