Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Attach temperature clamp to primary return above the pump as indicated
Use probe style temperature sensor for flow pipe above secondary heat exchanger
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Measure the temperature differential after the appliance has been
running for at least 2 minutes.
Expected differential approximately 25°c or less.