Set Appliance State:

Mains Power Off
User Control to Off Position
CH Demand
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

This test is for sealed systems only if the appliance is fitted to an open vented system please select "system pressure remains constant".
Allow burner to ignite and system to heat.
Observe system pressure gauge.
Does the system pressure stay constant?
Note:
System pressure should be at least 1.2 bar.