Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
CH temperature control set to MAX
Attach temperature clamp to the flow and return pipes
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the boiler to run for central heating and the system to heat up.
Measure the temperature differential.
Expect a differential of approx 20°C or less.
Note.
1. Ensure all radiators are open and system is balanced correctly to provide correct test results.
2. Initial temperature differential may be greater than 20°C when system is heated from cold.