Set Appliance State:

Mode selector switch to Off/Reset position
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Central heating temperature control set to maximum
Attach a U-gauge to the burner pressure test point
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Mode selector switch to CH position.
Allow burner to ignite and ramp up to full pressure and heat system to approximately 60°C.
Slowly turn the CH temperature selector to minimum position.
Does the gas pressure decrease as the burner modulates?
Note:
When U-gauge is removed pressure test point
should be tightened and checked for gas soundness.