Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Gain access to the PCB
Remove spark ignition lead from the spark generator and make safe
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if required (press and hold the reset button
until the chimney sweep button LED flashes rapidly, then
release the reset button)
Allow the 4 minute pump purge to complete.
Approximately 8 seconds after the fan has started a strong
consistent spark should be seen between the spark generator
output terminal and the PCB earth connection, this will occur
five times before ignition lockout occurs.
Is there a strong consistent spark?