How do I fix my Ideal FF350 Slimline Classic Boiler?

My Boiler the Ideal FF350 Slimline Classic was fitted in 2003. I have never encountered problems and it has worked extremely well up to now. I have been using the heating system all through the winter and just when we had the recent warm spell I turned off the central heating but left the water on the automatic setting. However with the recent cold snap again I have reset the heating to automatic, it comes on morning and night.

However I have now found that the radiators are not heating up and I have tepid not hot water. I have looked at the boiler when the heating system is timed to come on and the blue flame that you can usually see in the inspection glass is not ignited. I cannot see a reset button or anyway to fire it up. Any assistance you can give would be appreciated.