Nutone CV353 does not shut off, think it is the relay board

You may have a stuck relay or one of your access port switches may be bad. According to the owners manual: "A complete check of all Wall Inlet and Power Unit low voltage control lead connections (external yellow leads). Turn system off by removing fuse or tripping circuit breaker at
house fuse box."

Some units have an on/off switch on the power unit itself. Check to make sure that is not turned on. Unplug your power unit and remove the 2 low voltage wires (not the power cord itself) . The low voltage wires start at the unit and run throught your home and attach to each hose inlet. They are usually attached to the unit by simple wire terminals or wire capped to small wires coming out. Just unlug the terminals or unscrew the wire caps and pull the connections apart. Plug your machine back in. If it still comes on the problem is the relay or circuit board/switch/ relay assembly inside the unit. If it doesn't come on with the low voltage wires unattached then you may have two wires touching somewhere in the low voltage wiring.

http://www.centralvacuumstores.com/cvs/trouble_help.php#runs_continuously

Here is a link to help you find a local dealer:
http://dealer.nutone.com/DealerLocator.aspx?unit_id=002&cata_id=8

It sounds to me that the relay has stuck contacts. Try tapping the relay with the HANDLE of a screwdriver if you can find it. BE SURE TO UNPLUG THE UNIT BEFORE YOU OPEN THE UNIT !! Most centrals now have circuit boards and not seperate parts like earlier vacs which means you will have to replace the board.
Another thing to try is to take loose one of the low voltage wires to see if the unit will stop. If it does, you have a short with the wires touching somewhere along the line.
I hope that I have helped.
Joe

You have a defective internal relay on the vac. Check for warranty coverage as this is a common occurrence on these big box store units.
If beyond warranty the relay should be a straight forward unit, miniature circuit board type plug in device. Find a Broan Nutone service center or take to vac pro shop for parts.

the parts are available. go to:

NuTone Customer Service
Email or Call 888-336-3948
Hours: M-F 8:30 am - 5 pm EST

please rate my answer as a fixya!

Try to plug the hose in sideways. So the top of the hose is rotated 90 degrees. If the unit turns on then there is something wrong with the hose. It might be a short or it could be a bad switch on the handle. If the unit still wont turn on I would think that maybe the low voltage wire got disconnected from the unit or there is a break in the low voltage wire somewhere along the way. Let me know if you plugging the hose in sideways works.

You need to determine if this is a problem with the hose or the unit. I would recommend plugging my hose in the wall sideways. This should make your central vacuum run continuously. If the unit doesn't cut on and off it is the hose. If it still cuts on and off it is probably the relay.

It sounds like you could have one of two problems. I would guess either a short in your house, or a bad relay. If you plug you hose in sideways it will bypass the low voltage wire in the hose. If the unit doesn't shut on and off then you have a short and need a new hose. If the unit continues to cut on and off then you probably need a new relay. The relay is really easy to change out yourself and there are places to buy online.

My guess would be that the motor is done. Impossible to diagnose for sure without seeing it of course. If you were happy with the unit before the trouble, a replacement motor will probably run $250-$300. If you are interested in a new unit, shop around. There are definitely better designed and more powerful units out there, although some of them can cost quite a bit more than $300. Good Luck!!