Set Appliance State:

Mains Power Off
CH Demand
ON/OFF Switch ON
Summer/Winter button set to Winter
CH Temperature selector to maximum
DHW Temperature selector to minimum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler to ignite and run and system reach a reasonable temperature.
Slowly turn down the CH temperature selector.
Does the burner modulate down as the temperature demand is met?