Set Appliance State:

Mains Power Off
CH Demand
Mode Switch in LOW position.
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Run the boiler in its low operating mode.
Does the Burner shut off when the system reaches the low mode temperature setting (approx 68 deg C)?
Note:
It may be necessary to reduce the heating load by turning off some of radiators to reduce the time taken for this test.