Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
DHW Demand
Remove the electrode assembly
Position as Shown in the Diagram
DO NOT HOLD THE ELECTRODE ASSEMBLY
Ensure the earth wire is slid over the straight part of the electrode as shown
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to run and ignition sequence to commence, observe the electrode is sparking present at the electrode.
Note:
If the appliance locks out reset as necessary until the test is complete.