Boiler only 2 half years old.
Orange PCB appears to have failed (melted section)
Why or what causes this.

PETE, January 2011

These pcbs are notoriusly bad.
If, as you have suggested, it has melted, the pcb (obviously) will need replacing. But make sure the motor windings are tested for resistance BEFORE installing the new pcb, to ensure the new pcb won't go the same way.
These windings include fan, pump and gas valve.
From memory:
Fan should be about 110-130 Ω
Pump around 200 Ω
Can remember the gas valve resistance, but ensure it shows an Ω reading.

Carefree, January 2011