Set Appliance State:

Mains Power Off
Gas Off
Turn Hot Water Tap On
ON/OFF Switch ON
Summer/Winter button set to Summer
CH Temperature selector to minimum
DHW Temperature selector to maximum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow fan to run and observe the spark electrodes.
Is sparking present at the electrodes?