What Are the Causes of Vacuums Losing Suction?

Suction generated by a fan motor powers a vacuum cleaner as it pulls dirt through a chamber or hose and then deposits the debris into a bag or a cup. Some vacuum cleaners have a rotating brush or a beater bar at the end of a nozzle to help agitate and sweep dirt into the suction chamber. All of these areas must be free of obstructions and be working properly for a vacuum cleaner to remain 100 percent functional, or you will gradually lose suction.

Change the Bag:
The first place to look is the vacuum cleaner bag. When a bag is full or if it has become ripped or torn, there will be a corresponding loss of suction. Even if the bag looks intact but there is still a suction loss, change it for a new one. This way, you will know for sure that the bag is not the problem.
Clean the Filters:
Most modern vacuums have two filters. There may be a filter to keep dust out of the motor, or a pre-motor filter, and an exhaust filter. They may have a plastic frame surrounding a sheet of material, or there may be a boxlike container that holds a sponge type of high-efficiency particulate air filter. Most filters are washable and, once dried, can be inserted back into place. If they are damaged, they must be replaced.
Obstructions in the Vacuum Airflow:
The vacuum airflow begins at the tip of the hose in a canister vacuum cleaner and at the opening in the base of an upright vacuum cleaner. Stretch out a hose to full length and insert a broom handle through it. The handle will push any obstruction all the way through. Inspect the hose from end to end. Any crack, hole or kink will cause a vacuum to lose suction. If the hose is compromised in this way, it must be replaced. Conversely, turn an upright vacuum upside down to inspect the opening that leads up into the body of the vacuum. Look for pieces of paper or hair jams that might limit the suction. If the upright has a rotating brush, remove it to gain greater access to the opening. Also, check the connections between the hose and the vacuum. A bad or loose connection will allow the vacuum airflow to be compromised, and this will cause a loss in suction.
Check the Rotating Brush:
If the rotating brush, or beater bar, is not turning, it will seem like there is a loss in suction. The rotating brush sweeps dirt and debris into the vacuum suction airflow and makes it easier for the vacuum to pick up dirt. If the rotating brush is no longer spinning, there will be a corresponding loss of cleaning power. In most cases, the rotating brush can be removed and cleaned so that it functions normally again. Oftentimes, however, the drive belt that turns the brush may be broken and must be replaced to regain proper vacuum suction.
The Motor:
If the motor is going bad, the vacuum will lose suction. A bad motor may sound off key, it may smoke or it will run in fits and starts. Motors are not generally do-it-yourself jobs, and if the motor is bad, the vacuum must be replaced. On some bag vacuums, however, the motor uses a spinning plastic fan blade to achieve suction. The fan blade is attached directly to the motor axle. Dirt and debris pass through the blades and are pushed into the bag. If any of these blades have been broken, the motor may vibrate or run off key, leading to a loss of suction. Replace the fan blade if that's the case.