Set Appliance State:

Mains Power Off
CH Demand
Selector switch to heating
CH temperature selector to maximum
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to fire and system to heat while monitoring the system pressure gauge.
Does the system pressure remain stable at its charge pressure?
System pressure should be approximately 1 bar.