Set Appliance State:

Mains Power Off
CH Demand
Heating temperature selector to maximum
Hot water temperature selector to OFF
Gas On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to fire and heat system.
Monitor the system pressure gauge.
Does the system pressure remain constant?
(System pressure should be approximately 1 bar)
Note:
This test is for appliances fitted on sealed systems; if appliance is fitted to an open vent system, then select the "Pressure remains constant" option below.