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 image
Ensure only the metal part of the electrode mounting bracket is touching the appliance metalwork as shown
DO NOT HOLD THE ELECTRODE ASSEMBLY
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 tip?
Note:
If the appliance locks out reset as necessary until the test is complete.