Set Appliance State:

Mains Power Off
CH Demand
CH Selector in Maximum position
ON/OFF Switch in ON position
Summer/Winter in Winter Position (IN)
Timer Set to ON Position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

With the boiler cool check the system pressure is 1-1.5bar.
Allow boiler to ignite and CH system to heat.
Monitor the system pressure gauge as the system heats up.
Does the system pressure rise steadily to around 2 bar then settle as the central heating heats up?