Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Turn Hot Water Tap On
Remove diverter head from body by removing retaining clip located behind the head
Diverter valve located at the lower LH side of the appliance
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Is the diverter valve in the DHW position (Spindle extended out)?
Note:
CH position - Spindle retracted inside.
DHW position - Spindle extended out.
If the diverter valve is in the correct position then it is advisable to repeat this test several times as the valve could be sticking.