Set Appliance State:

Turn Hot Water Tap On
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow the appliance to run and reach operating temperature.
Test 1:
Measure the temperature of the hot water at the tap and make a note of the reading.
Test 2:
Measure the temperature of the hot water as it leaves the boiler (measure on the pipe leaving the boiler as indicated by the red arrow).
Compare the 2 readings.
Is the temperature at the tap approximately the same as the output from the boiler or is it significantly cooler?