Set Appliance State:

Gas Off
Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove the lower spark lead and make safe
Attach crocodile clip to the earth lead, pointing towards the spade for the ignition lead as shown
Gap between crocodile clip and the spade should be approx. 1cm
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Shortly after the fan begins to run can sparking
be observed between the crocodile clip and the
exposed spade connection?