Hello,
I think you are completely missing the point of the thermocouple. I strongly suspect that it is working correctly. I had the same problem and did all of the above except remove the thermocouple and still had the same problem. The one thing I didn't do was to separate the clear dirt can from the yellow can holder section and take air blast and blow out all the holes in the yellow can holder section. Once I did that the problem was solved.
(I think Dyson confused customers by claiming that a Dyson will not clog up).
What was happening was the motor got hot because the holes were blocked and it had to work harder to maintain suction. More work=more heat =motor shutdown. When the motor got hot the thermocouple did its job and shut down the motor. By inserting a thin membrane between the thermocouple and the motor, you have effectively insulated and circumvented the motor safety device that prevents the motor from overheating and burning up. Since your post is a couple of years old, I would be interested in finding out the end result on your machine.
Hope this helps.
John, August 2007