Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Gain access to PCB (use Insulation Mat as required)

Observation:

Move the jumper near the three LEDs from position 2&3
(Single LED mode) to position 3&4 (Triple LED mode), this
will enable full diagnostics via fault codes.
When mains power is switched on all three LEDs should flash for a few seconds, this can be used to confirm triple LED mode has been enabled.
Remember to set it back to single LED mode when diagnosis is complete.