Welcome to CS!!
Not sure where you could get it serviced, you can send one email that will go to all the sponsors, its at the bottom of the list of sponsors on the left. The ones that can help will get back to you.
Alternatively, you could service it yourself. Give it a descale and backflush, its probably all it needs and is quite simple to do yourself. Have you backflushed and descaled in the 3.5yrs you had it?