Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove boiler control unit from fire front & fit to
connector on the right-hand side of boiler
Ensure there are NO demands
Boiler On/Off switched On
Potentiometers set to fully clockwise position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Do both displays operate?