So, getting back to services. Your owners handbook (I assume you got one with the bike)[if not you can download a copy at
http://www.fiche-man.com/triumph/triumph.htm shows all the service intervals and what's included in those services.
Basically, the major services, which include the valve check, are every 12K. And the minor services, which is really just an oil & filter change, are in between at 6K, 18K, 30K etc.
The 18K service cost me £170 most of which was labour. You can easily do it yourself.