Set Appliance State:

Mains Power Off
Gas On; Pilot On
CH Demand
Boiler On/Off Switch ON
CH Switch ON
DHW Switch in INSTANT position
CH Temperature Control in Maximum position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

With the central heating operating does the system water pressure rise excessively?
Note: This test only applies to boilers installed on sealed systems, pass this test if boiler is installed on an open vented system.