Set Appliance State:

Gas Off
Mode selector switch to Off/Reset position
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
Hot water temperature control set to maximum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Mode selector switch to DHW position.
With a DHW demand does the fan run?