blockage,clogged filters,loose wiring in plug,broken wire in flex,faulty on/off switch or loose connection,loose wire on cap/balast resistor,loose wiring on motor,thermal cut off in motor faulty,or cutting in because of inadequate ventilation due to filter/blockage.the therm/co is in the motor.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix vacuum cleaners.