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 (max flow temp 82 deg C boiler should not go to overheat/lockout)?
Note:
It may be necessary to reduce the heating load by turning off some radiators to reduce the time taken for this test.