Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
If appliance has lead connected to front of burner ensure it is refitted
Gain access to inner combustion chamber
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as necessary.
Approximately 2 seconds after the fan starts to run
can sparking be seen at the ignition electrode(s).
Note:
Appliance may have either 1 or 2 ignition
electrodes depending on date of manufacture.
If lockout occurs turn power off and back
on to repeat test as necessary.