Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Remove the diverter valve actuator from the diverter valve body
Note:
The diverter valve motor can be removed without draining the appliance
Unscrew the milled ring and pull the motor assembly towards you
The assembly will slide free from the valve
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

There are two styles of diverter valve motor that may be fitted to this appliance. For this test the operation is the same.
Watch the diverter valve actuator movement.
1) The actuator should move to its longest position (CH) and then back up to its mid position freely - shortest position is DHW position.
If the actuator only moves up (i.e. was at rest in the lower position) then repeat the test by turning the mains power off & on and watch the actuator move again when it should behave as above.
2) Turn On hot tap, the actuator should now move to its shortest position.