Set Appliance State:

Mains Power Off
CH Demand
DHW Selector in Minimum (-) position
CH Selector in Maximum (+) position
ON/OFF Switch in ON position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Allow boiler to ignite and CH system to heat.
Monitor the system pressure gauge as the system heats up.
Does the system pressure remain constant at about 1 bar as the central heating heats up?