Set Appliance State:

User Control to Off Position
Isolate Mains Power to appliance as per TOPs P4
Ensure DHW is calling for heat
Attach U-gauge to pressure test point (left hand side of fan)
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

User control switch to ON position.
Allow fan to run and burner to ignite.
After approximately 20 seconds does the pressure ramp up to 8 mb?
Note:
When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.