There are people on here - well meaning I'm sure - who will tell you that to service your own boiler is illegal and insist that you must be Gas Safe Registered to comply with the law to undertake this. They are wrong...
You must be Gas Safe Registered to accept payment for work on gas appliances but a householder only needs to be competent and the regulations do not define competence. Landlords doing own maintenance do break the law unless thay can provide a safety inspection document from a qualified specialist - an annual requirement.
This Wikipedia article helps understanding...
http://en.wikipedia.org/wiki/Gas_Safety_(Installation_and_Use)_Regulations_1998
And the The Gas Safety (Installation and Use) regulations 1998 can be found here...
http://www.opsi.gov.uk/si/si1998/98245102.htm#1
As for the wisdom of doing your own service that is entirely another matter - it won't cost much to have a specialist do it - you can watch and take notes and do it yourself next time perhaps.
Good luck...
Peccavi
December 2009