Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach temperature clamps to the flow and return pipes, due to access a clamp cannot be fitted to the return pipe above the pump, so either use a probe or alternatively attach a clamp to the return pipe under the pump
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.
Expect a differential of approximately 20°C or less.
Is the temperature differential as expected?
Note.
Initial temperature differential may be greater than 20°C when system is heated from cold.