Set Appliance State:

On/Off Switch OFF
DHW Demand - Ensure Store is not up to Temperature
Isolate Mains Power to appliance as per TOPs P4
Move the diverter valve lever to the mid position - push lever towards the back of the appliance with a downward pressure on the lever and it should lock into the manual position
Disconnect connector J7 (diverter valve lead) from the PCB and make safe this is important to stop the valve from driving to the DHW position
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Appliance On/Off switch On.
Reset lockout as necessary.
Allow boiler to fire and run.
Does appliance still kettle?