Basic troubleshooting steps
There are a few issues that can cause a central vacuum system to have low suction.
You will want to first check the suction directly at the power unit to determine if the unit is the problem, or if there is a clog somewhere else. If the unit has great suction, then the clog is in the pipes or the hose. We have more detail instructions on removing a clog that is in the pipes or hose available.
Is your central vacuum bag over three-quarters of the way full?
If you have poor suction at the unit, the first thing you can check is your central vacuum bag. If the bag is three fourths or more full, replace the bag and test the unit again.
Are the filters and screen free of debris?
If the vacuum bag is not full, or if replacing the bag did not work, check to see if the cloth filter, foam filter, and screen is clean and free of debris. Sometimes there are secondary filters past the initial filter. If the secondary filter appears clogged, try cleaning it off or replacing it before testing the unit again.
Are the power unit gaskets in good shape and properly installed?
Another step you can take is to check that the power unit gaskets are in good condition and correctly installed. There is usually a large gasket that joins bottom-emptying buckets to the vacuum body.
Does your system contain more than one motor?
If your system has more than one motor, it is possible one of the motors has failed. In this case, you will need to get a replacement motor. It may appear that a motor is working because it is spinning, but it may just be the air flowing through it. If you test a motor, be sure it runs without shutting off for 20 minutes.