Diagnosis
A blockage exists in the airflow path after the dust cup. The most common locations are the hose, the hose inlet on the vacuum body, or the opening behind the dust cup.
How to Fix It
Follow the air path. Remove the dust cup and hose. Shine a light into the hose inlet on the vacuum body. Check for a clog. Reattach the hose to the vacuum body only (not the floorhead). Turn on the vacuum and place your hand over the hose end. If suction is strong, the blockage is downstream in the floorhead or wand.
If That Didn't Work
The hose itself may have an internal leak or tear. Detach it completely. Visually inspect along its entire length for cracks, especially at the bends. Listen for hissing air while the vacuum is running.
Heads Up
Weak suction is almost never the motor on this model. It is a sequential checklist: dust cup full > filter dirty > hose/wand clog > hose leak > floorhead clog.