Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the cap from the spark electrode
Unscrew it anticlockwise from the ignition lead

Observation:

Inspect the end of the ignition lead.
Is it in good condition with a tight bundle of copper strands for the cap to screw into?
It should look like the image shown.
Note:
Do not refit the spark cap if the ignition lead is in good condition.