Vacuum won't turn off

Check connection from hose to the main unit. Very important to make sure that the hose has a solid connection to the front of the machine. If not, then the receptacles can't make good contact to allow the power nozzle to turn on.
RainVac
www.rainvac.com
800-523-0510

Depending on the power nozzle model, does a red light come on the top of the power nozzle? If it does, then the problem could be the circuit breaker. If it does not, then the problem could be either in the hose or the connection from the hose to the main unit. Make sure you hear to clicks and the hose is connected solid to the main unit. Otherwise, the receptacles can't make contact to allow the power nozzle to turn on.
RainVac
www.rainvac.com
800-523-0510

Be sure to have a solid connection and that you hear two clicks when connecting your electric hose to the front of the main unit. If this connection is not solid, then the receptacles can not make contact. Try bypassing the hose and plug your power nozzle directly into the front of the main unit to confirm that the hose is the issue.
RainVac
www.rainvac.com
800-523-0510

The power head requires 120 Volts. Some hoses have a receptacle in the handle for the power head plug, and the hose has a cord at the wall inlet end that plugs into a receptacle. Some hoses have a plug at the wall inlet end that plugs into a 120Volt receptacle built into the inlet. The hose plugs into this receptacle when you push the hose into the inlet. The power for this built-in receptacle is wired with line voltage when the system is installed.

Have you checked the hose for clogs or leaks. Clogged and leaky hoses are an area of concern with any central vac. Unless you hose has a hose sock, then wear and tear from constant rubbing on floors and other surfaces will result in holes and cracks. Pulling the hose can also result in leaks where the hose attaches to the handle and intake connector.
Mix some dish soap with water.
Use shop vac to blow air through hose, with other end capped or "clogged".
Apply soap solution to each end of hose.
If bubbles form, this indicates leakage. Hose will need to be replaced.

If there is a switch on your hose, it may be broken.
Your system powers on from the inlets via two low voltage wires that run from the inlets to the switch/relay at the power unit. Each inlet has 2 spring loaded pins attached to the low voltage wires. In the photo below you should see these pins at the bottom of the opening, just above the door hinge. The receptacle at the top of the inlet in this photo supplies 110 volts to power your power nozzle. Not all inlets have this option, but if yours does, exercise extreme caution. Your hose must have a completely metal end or if it is a plastic end, it must have a metal band in order to short the 2 low voltage wires together to trigger the switch.
You can manually short the two low voltage pins together by using a metal pipe or needle nose pliers, just touch both pins at the same time. CAUTION: stay away from the 110 volt receptacle if present.
If your system powers on with this manual method then it would seem that the problem is in your hose.
If your system does not power on; your low voltage wires may be disconnected from the power unit or disconnected somewhere else . It's also possible that you have a bad circuit/controller board in the power unit.

Make sure cord is not damaged. Check to see nothing is blocking hose or carpet nozzle(where beater brush is or brush roll). Plug unit in to a receptacle that you know has power going to it. (Lamp you know works when plugged into same. Using hose on front, make sure bag bottom completely attached to exhaust, the hose has a little arm like thing that will depress the safety switch on the front of the unit, and turn on using foot switch at the back of the unit. If these do not work, it could be one of two safety switches, dirt may have fouled or switch may need to be replaced. Authorized Kirby Dealer in your area: Replacement parts, Kirby Distributor, call: 1-800-437-7170 United States and Canada

check the electrical contacts around the tip of the hose.Check another wall inlet around the house and see if it starts.If it does starts in another inlet than there is a problem with the wiring at the inlet where is not starting.If the vacuum does not start in any inlet check the power button at the vacuum location and the fuse.Also I should mention that if your brush have an on and off button you should check that is on.

Sounds like the relay that is in the central vac unit is stuck to the ON position. When you plug it back in..does it start right up ? If so.. You should be able to disconnect all the receptacle feeds to the central vac unit at the central vac unit to determine which one ( if any) is calling for the vac to stay on.. if none are.. then it is internal to the vac and may be a stuck relay... Hope that gives you some ideas to check...

Sounds like you have a clog, either in the hose, or the inlet down at the bottom. When there is a clog, the red light will come on and may also shut down to protect the motor.