To check for clogs, feel for suction at the end of the hose. If suction is low at the hose, the 3 filters are clean and the dirt-cup is empty, most likely there is a clog in the hose.
Lift-Off is a "clean-air" system where all the suction occurs through the hose. Check the hose for possible clogs by removing the hose completely from the back of the machine by the two screws at the hose cuff. Once it is completely removed, use a broom stick handle to push any dirt or debris through the hose. Remove the plate from the bottom of the machine and the brush roller.
Check the belt for wear or cracks and the brush roller for string or debris. Clear the air passage once the plate and brush are removed. If the unit suctions from the hose but not through the floor, lift the canister off the vacuum and set it aside. Recline the handle and turn the handle/foot assembly over so the underside of the foot is facing up. This will straighten the lower hose and allow you to look through the suction opening straight through to the brush.
If you need additional assistance, please take your machine to a local BISSELL Authorized Service Center. You can locate a Service Center online or by phone, 24 hours a day, by calling 1-800-237-7691 and choosing option #1.