Set Appliance State:

Mains Power Off
CH Demand
Boiler ON/OFF switch ON
CH temperature selector to Maximum
Room thermostat (if fitted) calling
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

This test is only for boilers fitted on a sealed system.
Pass this test if boiler is fitted on an open vented system.
Allow boiler to ignite and CH system to run.
Monitor system pressure on gauge in control panel.
After system has been running for a short while does the system pressure remain constant?
Note:
Initial system pressure should be approximately 0.5 - 1.0 bar.