Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Unclip diverter valve motor and pull left until it hits the gas valve
To unclip - Place screwdriver as in picture then twist
anticlockwise to unseat diverter
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Inspect the diverter valve motor, does it move to the fully retracted position during a hot water demand?
Note:
Diverter motor can be removed & refitted with gas valve in situ
but this should not be necessary unless motor requires replacement.