Why does my Dyson DC07 overheat and cut out?

This is a very common problem with the DC07 and a very straight forward one, your machine is being starved of air and the motor (which relies upon a constant airflow across it) is getting hotter, the bi-metallic cut-out, linked into the power supply heats up, expands and disrupts the current flow to the motor. This is why after a short period, the machine begins working again. Be very sure, your motor will not last very long under such a condition. A quick principal of operation (looking at your machine from the front): when you switch on, the motor uses up the air contained in the clear plastic chamber, the air is drawn down the right hand duct, through the filter past the motor (flowing over the carbon brushes) and out ot the vent under the clear bin. Simultaneously, air is drawn in through the wand if the machine is in the upright position, and travels up the left hand duct and into the clear bin. The dirty air is spun around the bin (like a motorbike on the wall of death) and the heavy dirt and debris falls to the bottom of the bin. When you tip the machine for conventional vacuuming, the valve on the lower left of the cleaner moves forward and the air is now drawn in from the bottom. Therefore, the right hand duct should always be clean air. If it is not, then the cyclone is not being allowed to spin the debris out of the air because it is not travelling fast enough. Something is preventing the motor from working at its normal capacity. The motor is driven by carbon brushes, therefore it will either run at full speed or it will stop completely if the brushes have worn out. If the motor is running, one can assume that it is okay. Unless, because it has been allowed to overheat in the past, there is some degree of arcing now present. One of the reasons behind this problem is the brushes overheating and starting to break up at the surface. Obviously, there is only so much 'first aid' the average owner can do, so this guide has been written on the basis that the unit is in some way blocked by foreign objects such as screws, paperclips, coins, fluff etc and assumes that the motor is serviceable. In the case of large objects, it is well documented by the manufacturer how to resolve this. Namely, by checking the u-bend at the back and the removable valve on the lower left. Its the problems caused by fluff that the guide concentrates on. Check the washable fillter (next to the motor) for debris build up; Incidently, a very common oversight by Dyson owners is to only wash the sponge insert. It is normally the yellow outer casing that causes the problems. Hold the filter outer casing up to a light source and you will likely see that it is blocked as you should see light through it when it is clear. Also, when you fill the yellow casing up with water, the water should instantly drain out.