Set Appliance State:

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

Observation:

Run the boiler in its High operating mode.
Does the Burner shut off when the system reaches the high mode temperature setting?
Note:
It may be necessary to reduce the heating load by turning off some radiators to reduce time taken for this test.