Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Selector Switch to Hot Water and Heating
Appliance CH thermostat set to MAX
Attach temperature clamps to flow and return pipes as indicated by the red arrows
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow boiler and system to heat.
Measure the difference in temperature differential.
Expect a differential of approximately 20°C or less.
Is the differential measured as expected?
Note:
Differential may be higher on initial start-up, allow boiler to run until return pipe starts to heat or the boiler shuts down before selecting an option. Turning off some radiators may reduce time taken for this test.