Set Appliance State:

Mains Power Off
CH Demand
Boiler ON/OFF Switch OFF
CH Temperature Selector to Max
DHW Temperature Selector OFF
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Boiler ON/OFF Switch ON.
Allow Boiler to fire and start to heat. Observe System Pressure Gauge on the 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 0.5-1 bar.