Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Remove diverter valve motor from diverter body
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Is the diverter valve motor spindle in the CH position i.e. fully extended?
Note:
It is recommended to ensure the boiler has definitely fired for CH demand before checking the position of the spindle as the boiler incorporates a built in delay.