I'm not a boiler engineer but I have the same boiler (and had the same problem). The most liklely cause is you need to replace the thermo-coupling unit. It sounds scary but is in the boiler engineers top ten 'easy money' jobs!
When you open the door and look at your boiler, it's the copper pipe you see going to where the pliot light is (in fact one end of it is the pilot light!). You can buy them at a plumbers merchant for little more than a fiver and they are dead easy to fix on - you just need a couple of small spanners.
A less likely cause would be the gas valve. If the above doesn't solve it then you might have to call a boiler engineer, but I'm pretty confident it will work. It usually does.
Good luck!
David, November 2008
