Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect the leads from the spark electrode
Carefully remove the electrode from the combustion box door
Disconnect the leads from the spark electrode
Carefully remove the electrode from the combustion box door
Measurement:
Measure the resistance between the tip of the spark electrode and the lead connection point.
Expect continuity/ zero resistance.
Note:
Before reassembly check the integrity of all disturbed gaskets and seals and replace as necessary.
Expect continuity/ zero resistance.
Note:
Before reassembly check the integrity of all disturbed gaskets and seals and replace as necessary.
Isolate as per TOPs P4
and refit as necessary