Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the outer and inner casings
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Does either the pump or fan run, signifying the boiler is carrying out its self-check?
Notes:
1. The fan can be very quiet on this appliance.
2. The pump can be very quiet so it may be necessary to confirm by gently pressing on the centre screw until it makes contact with the impeller (if it is running a grinding noise will be heard).