Isolate Mains Power to appliance as per TOPs P4
Remove electrode assembly

Observation:

Thoroughly check spark electrode for cracks and damage to the electrode ceramics and good general condition.
Check for correct spark gap, gap should be 4 mm +/- 0.5 mm.
Refit assembly after test.
Note:
Before reassembly check the integrity of all disturbed gaskets and seals and replace as necessary.