Set Appliance State:

CH Demand
Boiler On/Off switched On
Potentiometers set to fully clockwise position
Ensure boiler is cool
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance if required.
With CH demand does the fan run? (see note)
It may take up to 60 seconds for the fan to start when a CH demand has been applied.
Note:
If a fault code occurs during test click HERE.