Set Appliance State:

Mains Power Off
Turn Hot Water Tap On
Gas On
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as required.
Monitor the appliance as it goes through its ignition sequence.
Does the burner ignite and establish correctly?
This is confirmed when the flame symbol appears and remains on the left hand side of the display.
If the flame symbol does not appear after the burner ignites this indicates a rectification issue.
Once lit the flame should not baffle or be excessively noisy as this indicates a combustion issue.
Note:
The burner and spark electrode can be viewed by looking up through the sight glass on the front of the appliance.