Cause of CelticPlus Boiler Ignition out [electric fault]?

I have a celticPlus Boiler which suddenly stopped working and ignition light is out. I went throught the manual and first thing i found was that there is no electricity coming to the boiler. Obviously it was fuse. I replaced the fuse and it was confirmed that previous one was blown. After replaceing the fuse the timer is working and running but there is no fan sound coming from boiler and i cant even ignite it. The ignition system is such that I have to press the flame on for about 14 seconds and then it ignited. I have tried this but I know there is something I am missing. What might have caused the fiuse to blow? and after replacing the fule what i might check step by step to see if i need to call someone special or is it just a minor problem that I can fix.