Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
CH temperature control to max
Set selector switch to ch/dhw
Attach temperature clamp to flow pipe close to the overheat stat
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the burner to ignite and heat up the system
until MAX temperature is reached.
Monitor the appliance temperature.
Note:
To reduce the time for this test the heating load can be reduced
by turning off some radiators temporarily.