Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Adjust DHW flow rate to approx. 5 litres/min
DHW Temperature Control set to approx. 12 o'clock position
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 burner to ignite and establish.
As the hot water starts to reach temperature does the burner pressure modulate down to maintain temperature?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.