Set Appliance State:

Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4

Measurement:

Is the diverter valve flow adjuster open sufficiently?
With the hot tap fully open alter flow adjuster screw between fully open and fully closed and back to fully open.
Note:
Flow adjuster is situated on the outlet of the diverter valve there is 1/4 of a turn between fully open and fully closed. There is a groove cut in the head of the adjuster when this is in line with the outlet it is fully open.