Set Appliance State:

Mains Power Off
CH Demand
CH Selector Switch On
Gas Control Knob in Main Burner position
Gas On; Pilot On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the Main Burner alight, vary the boiler CH Temperature Potentiometer setting. Does the Main Burner cut out when the Boiler temperature reaches the Potentiometer Setting and re-ignite when the Potentiometer setting is increased?