Diagnosis
The floorhead height setting is incorrect, or the agitator (brush roll) is not making proper contact with the carpet. This model has a manual dial, not automatic adjustment.
How to Fix It
Locate the dial on the floorhead. For medium pile carpet, it should be set to position '2' or '3'. Set it to the highest setting ('5') and make a pass. Then set it to '2' and make a pass. Listen to the motor sound; it should load slightly on '2'. Adjust until you hear the brush roll engaging the carpet fibers.
If That Didn't Work
The brush roll bristles are worn down. Remove the floorhead and inspect the brush roll. The bristles should be stiff and approximately 1/2 inch long. If they are matted or less than 1/4 inch, replace the brush roll (part #161-0542). Worn bristles cannot agitate debris loose.
Heads Up
Always turn the dial to the highest setting ('5') before pushing the floorhead under furniture. Dragging it on a low setting against a thick rug or obstruction will stall the brush roll and burn the belt.