Set Appliance State:

Mains Power Off
Gas On; Pilot On
CH Demand
Selector switch to CH CONTINUOUS position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to fire and CH system on heat while monitoring the system pressure gauge.
Does the system pressure remain stable? (Minimum CH system pressure 1 bar)
Note:
If power has been switched off or CH demand has been interrupted, there will be a delay of between 1 and 3 minutes before the boiler starts.