Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Selector switch set to CH/DHW position
Boiler CH thermostat set to MAX
Attach temperature probes/clamps as indicated by the red arrows
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the appliance to run for 2-3 minutes then measure
the temperature differential.
Expect approximately 22°C or less.
Note:
To reduce the time for this test the heating load can be reduced by turning off some radiators temporarily.