Set Appliance State:

Mains Power Off
CH Demand
CH temperature selector set to MAX
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.
Choose "system pressure remains constant" if boiler is fitted on an open vented system.
Boiler ON/OFF switch ON.
Allow boiler to ignite and CH system to run.
Observe system pressure gauge on control panel.
After the system has been running for a short while
does the system pressure remain constant?
Note:
Initial system pressure should be approximately 0.5-1bar.