Lighting Baxi WM532 RS CHP?

Hi there, I am wondering if you can assist me, I have been trying in vain to relight the above model boiler. The boiler ignites when the grey button is pushed in and black button pressed, I have tried holding for 20 seconds (and on occassions a lot more than this) but as soon as the grey button is allowed to depress, the pilot light goes out? any help would be greatly appreciated, kids are freezing?

Jason
November 2006