Set Appliance State:

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

Measurement:

Allow boiler operate until noise begins.
Measure the temperature of the flow and return pipes as close to the boiler as possible and ascertain temperature difference between flow and return.
Expected differential 20°c or lower.
Notes:
To reduce the time for the test the heating load can be reduced
by turning off some radiators.
Differential may be higher at initial system start up.