Had mine done in 2012 a few months out of warranty at no cost - goodwill from Triumph.
As has been said, this is mainly down to your dealer, did you ask about warranty before they took the job on? If you didn't they would have diagnoses and replaced it without contacting Triumph - goodwill repairs have to be agreed with Triumph before the jobs done, it might be too late for you now.
Have to say if your dealer didn't talk to you about this at the time they are lacking and I wouldn't go back to them again - this is a well known problem with the previous generation TPS.
Edit:
Looking at your profile you come from Dorset, are you dealing with Total Triumph in Taunton, if you are I'm surprised you weren't treated better - always thought they were OK. Bridge Exeter did mine.