Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Programmer or selector switch set to hot water only
Hot water temperature selector to maximum
Heating temperature selector to OFF
Ensure heat bank is not up to temperature (this can be achieved by running the DHW with the mains power to the appliance on and the gas to the appliance turned off)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan to run and ignition sequence to commence.
Can correct sparking be seen between electrode tip and the pilot burner?