Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Unclip diverter motor and place in a safe location where spindle can be observed
(pump may need to be pushed slightly upwards to allow removal)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow ignition sequence to begin and burner to ignite and establish.
Isolate Mains Power to appliance as per TOP's P4

Gently push the diverter motor spindle with a screwdriver.
Is the diverter valve motor spindle
in the CH position - fully retracted?