Hotpoint TVM560 stops early and starts overheating?

Hi

My Hotpoint TVM560 is a year old, a few months ago it stopped, however I didn't go straight to it to unload it, after about 5 mins, I noticed a bad overheating smell, I rushed over to the dryer and found it was stopped at 20mins to go and making a quiet clicking noise, I quickly opened the door and it stopped.
Called the repair guy out and he said it was overheating because we had an extension on the air pipe, changed the switch as well but said it was our own fault.
We removed the extension and the dryer seemed to be ok for a couple of weeks, but now its doing it again, usually stopping around the 20min mark, but sometimes it will stop a fraction before the 0 mark and starts to smell.
Most times its fine the 1st run, but if i do a 2nd shortly after it does it again.
Anyone know what could be causing this problem?