Although this generally indicates that the bag is full, it may be caused by other problems. If you have fine dust in your area, the bag may seem like it's not full, but the pores in the bag are clogged so the vacuum will shut off as if the bag is full. This can be partially solved by setting the dial on top to the smallest dot.
The problem could also be caused by a dirty afterfilter. This filter is located beneath the tool caddy on the back of the machine. Access is gained by pressing the tab on the back of the machine and lifting the caddy. If dirty, replace it. If you don't have a replacement, check to see if the vacuum will run without it. It should if there is not other problem causing the vacuum to not run.
Third, try detaching the hose, turn the machine on to see if it runs. If it does, place your hand over the in port. If the vacuum shuts off, the problem is most likely a broken, worn, or clogged Control Valve Assembly. This is the part the dial connects to. This is a problem that should only be repaired by an authorized Aerus Electrolux service tech. If you have been using generic "Made to fit Electrolux" bags, the motor and interior of the machine should be cleaned. This is worth doing as there should be a long "life" ahead for the vacuum. Periodic maintenance should be done.
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It could also be caused by loose connections, worn or broken switch/es, broken wires, or bad motor. This can be narrowed down at the shop.