Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove 1 wire from the modureg and make safe
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as necessary (Control knob to reset position for then release).
Allow the fan to run and observe the burner and spark electrodes through the viewing window.
Does sparking occur and the burner ignite and establish smoothly?