Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
DHW flow rate approx 9 litres/min
Attach pressure gauge to gas valve pressure outlet test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to ignite and establish.
After approximately 45 seconds set hot water temperature
control to number 2 position.
Does the burner pressure reduce as the demand is met (modulation)?
Note:
1. At end of test return temperature control to MAX position.
2. When pressure gauge is removed the pressure test point
should be tightened and checked for gas tightness.