Given that the thermal cutout is inside the machine it will be self resetting - the thermal trip may be defective and not resetting itself -or- something other than the thermal trip may be defective (cable, switch, motor).
People on E-bay sell these things for £3.40 with different suppliers charging varying amounts for postage.
dysonmedic.com has nice pictures and instructions showing how to strip and reasssemble dysons.
Good luck...
Peccavi, September 2009
