Set Appliance State:

Mains Power Off
CH Demand
Selector switch set to CH position
Boiler CH thermostat set to MAX
Ensure CH controls are calling for heat
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the burner to ignite and run in CH mode.
System pressure should be 1 to 1.5 bar ( when cold)
Does the pressure remain stable or is there
excessive system pressure rise?