The standard warranty is 12 month, which is convenient seeing as boxes go kaput just after.
Anyway ring sky and they'll say its £65 for an engineer callout, take out insurance, or get it repaired locally.
Or do what i did. Ask to go through to cancellations and threaten to leave as you're not happy about paying to get it repaired. 5 mins later. The engineer was booked and they been out and replaced my 2 faulty HD boxes.
If they fob you off just hang up and try again.
Cant promise it will work but you can only try mate.
The guide linked to above is a really good one if you want to self repair your Thomson (which is the best option IMHO).
All the information you need to decide what is best for you is contained within this post I wrote about a year ago (lots of us have been there before you so there is plenty of help available on here if you need it).