Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Refit combustion chamber if this has been removed to check fan operation
DHW temperature set to MAX
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Observe through the sight glass, does the
burner ignite smoothly and establish?