My vaccum cleaner may have a faulty thermal cut out switch?

My upright Hoover U3525 vacuum cleaner cuts out after a few minutes, it's very new and all the filters, tubes etc are totally clear of blockages. I'm told this may be down to a thermal cut out switch which sits near the motor and is hard to get to. Having rang Hoover they can't help as my receipt has vanished of the face of the planet. Is replacing the thermal switch an option or would I have to get a new motor? Can an amateur like me replace the motor or do I need to take the item to get repaired - I'm informed this is about as dear as a new vaccum cleaner.

Mark
June 2008