Set Appliance State:

Mains Power Off
Gas Off
CH Demand
Pre-heat switch OFF
CH temperature set to maximum position

Gas On
Mains Power On

Observation:

Allow boiler to fire and heat system.
Observe system pressure gauge.
Does system pressure remain constant (system pressure approximately 1bar cold).
Note: This test applies to sealed systems only, pass this test if appliance fitted on open vented system.