Central vacuum systems are a wonderful cleaning convenience. Regardless of the model you own, you want a unit that is reliable, efficient and one that you can generally service and maintain yourself. If you have a system that will not shut off, the first objective is to get it shut off. You can then troubleshoot it and repair what is wrong. Following a few steps will get the vacuum turned off and allow you to troubleshoot the entire system.
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Check each inlet while the unit is running. Unscrew each inlet faceplate from the mounting bracket one at a time. Watch and listen each time you back out the screws of each faceplate. See if the system shuts off when you back out the screws which hold the low voltage wires in place at each inlet location.
Remove the valve at the inlet location where the system shuts off. Reverse the wire at this inlet; then, screw the faceplate back onto the mounting bracket. Do so carefully so as not to constrict the reversed wiring too severely.
Check the wire if the all the inlets prove to be functional and problem free. Access and trace the wire wherever the wire and pipe can be seen, in the attic, crawlspace or basement. Look for any wire damage or wire short caused by rodents or other service work and repair any damaged or severed wiring.
Confirm that the switch is indeed off. Flip it two or three times to be sure; then, turn it to the off position. Disconnect a low voltage wire from the body of the unit itself. Replace the bad relay if the unit continues to run with one of the wires disconnected from the body of the unit.
Trace and replace the system wire if the unit cuts off when the wire is removed, but comes back on when the wire is reattached. Refer to the wiring diagram for the unit to trace it. Call a service technician if you are not comfortable doing this kind of repair, or if your warranty may be an issue.
Check the bag or canister if you notice a severe reduction in airflow or suction strength. Empty the canister or bag if you find it full. Examine the filter bag for any holes or tears if you find it not to be full. Look at the secondary filter to see how dirty it is, and clean or replace it, if the bag is fine.
Verify that the vent system is not blocked or otherwise clogged with lint and debris once you have cleared the bag or canister as the culprit. Double check the canister and snap shut any latches after looking to be sure it is installed correctly.