How can I get my Potterton Profile 80e to ignite?

The query relates to our Potterton Profile 80e boiler. We replaced the circuit board earlier this year as we had had problems with the boiler not lighting during October last year. It has worked fine until yesterday when we found that the pilot light has gone out and although it is sparking it is not lighting the pilot so the boiler is not firing up.
The boiler was only going on once a day to heat the water and I recently changed the timer (about 3 weeks ago).Before that it was going on twice a day timed. When we had our problem in October we had turned the boiler off during a mild few days as we were away.After we got back we could not re-ignite the boiler and after much work by a CORGI reg engineer a new circuit board seemed to do the trick.Now we seem to have the same problem again. Is there any way to ignite the pilot? Alternatively,is it the gas valve not opening or is it something to do with the pilot light assembly? Or is it something else? Please can you help?