If you are lucky it may just be a worn out thermocouple or maybe a choked pilot jet or the gas valve may have gone faulty and require replacement, if you haven't had the boiler serviced on a regular yearly basis then a service will be required and any other worn parts replaced,fans,pressure switch, thermistors and safety stats are all parts that wear out after a few years, your oher option would be to replace your boiler with a new high efficiency boiler without a pilot, cheaper to run and better for the planet.