Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the burner from the boiler

Observation:

Inspect the spark electrode assembly and earth pin, ensure the ceramic is in good condition.
Place a straight edge across the top of the heat exchanger above the spark electrode and ensure the electrode is 3mm +/- 1mm below the edge.
Note.
1. Ensure that when removed care is taken not to damage the ceramic face of the burner.
2. Before refitting the burner inspect the sealing gasket and replace if damaged.