Same thing with mine. But I've been told that it's the thermal cut-out switch. This activates because the filter below the dust canister is blocked and the motor overheats. the thing is that once this happens it destroys the thermal cut-out switch within the motor and the motor has to be replaced. On mine, the filter was clean but the the thermal cut-out activates after about 10 mins. I will have to replace the motor. Cost £70 GPB at the local repair shop
Steve Carpenter, August 2006