Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamps to the flow and return pipes
If there is no access to remove the right hand side panel then you will need to use a temperature probe on the return pipe instead of a clamp
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the appliance to run for central heating and the system to heat up.
Measure the temperature differential across the flow and return pipes.
Expect a temperature differential of approximately 20°C or less.