Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Selector switch to heating
CH temperature selector to maximum
Attach a pressure gauge to the burner pressure test point
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to fire and heat the system to a reasonable temperature (approximately 65º C).
Slowly turn down the boiler CH thermostat to its mid range setting.
Does the burner pressure reduce as CH temperature meets demand temperature?
Notes:
1. It may be necessary to reduce heating load by turning off some radiators to reduce time taken for this test.
2. When pressure gauge is removed the pressure test point should be tightened and checked for gas tightness.