Get your wallet out time, usually the PCB 150.00+vat plus fitting
Try dropping down the controls flap, you will need to remove the front cover two screws underneath and lift off then see if the boiler fires by opening a tap. Some i have experienced work while the flap is down, not ideal but sometimes works.
These are a crap boiler, they have a crap filling loop that sticks noisy gas valve, change it if you have the money
Ray, May 2009