You didn't mention the model, but with several Electrolux canister models, I'd say there's probably a problem with the control valve assembly inside the canister. This would need to be repaired at an authorized Aerus Electrolux store. If unsure where the nearest store is, use this link to locate one: http://www.aerushome.com/storelocator/
The tip on the following link covers other possible causes.
Answers & Comments
You didn't mention the model, but with several Electrolux canister models, I'd say there's probably a problem with the control valve assembly inside the canister. This would need to be repaired at an authorized Aerus Electrolux store. If unsure where the nearest store is, use this link to locate one:
http://www.aerushome.com/storelocator/
The tip on the following link covers other possible causes.
http://www.fixya.com/support/r7367127-electrolux_epic_6500_trouble_shooting