When a central vacuum will not turn on, the fault is in one of four places: the power to the unit, the unit itself, the low-voltage wiring and inlets, or the hose. A short jumper wire across the unit’s two low-voltage terminals sorts the first two from the last two in a single step. Work through the sequence below in order; most dead systems are a tripped breaker, a tripped thermal cutoff, or a loose terminal at one inlet, and none of those cost anything to fix.
The test sequence
| Step | Test | Result | Meaning |
|---|---|---|---|
| 1 | Plug something else into the unit’s outlet; check the breaker | Outlet dead | Breaker or outlet fault |
| 2 | Let the unit cool; press the reset button | Unit starts | Thermal cutoff had tripped; find the cause |
| 3 | Jumper across the unit’s low-voltage terminals, house wire disconnected | Starts | Unit is fine; fault is in house wiring, inlet, or hose |
| 3 | Same | Does not start | Fault is inside the unit |
| 4 | Jumper across each inlet’s contacts | One inlet fails | That inlet or its branch wire |
| 4 | Same | All fail | Trunk wire or splice near the unit |
| 5 | Hose plugged into a known-good inlet | Does not start | Hose end, hose wiring, or handle switch |
| 6 | Unit hums or clicks but motor does not spin | Hums | Motor, brushes, or seized bearing |
| 6 | Relay clicks, motor silent | Clicks | Motor circuit, brushes, or thermal cutoff |
| 6 | Nothing at all with the jumper | Silent | Relay, circuit board, transformer, or cord |
Step 1: Power to the unit
Plug a lamp or a drill into the unit’s receptacle. If it is dead, check the breaker; central vacuums are often on their own circuit, and a tripped breaker on a rarely used circuit goes unnoticed. If the breaker is fine and the receptacle is dead, or the breaker trips again as soon as it is reset, stop there and have a licensed electrician look at the circuit. Do not keep resetting a breaker that trips.
Step 2: Thermal cutoff
Most power units have a thermal protector that shuts the motor off when it overheats. The usual causes are a clog, a full bin, a loaded filter, or a blocked exhaust, all of which make the motor work harder and run hotter. Unplug the unit, let it cool for 20 to 30 minutes, press the reset button if it has one (often near the low-voltage terminals or the cord), and plug it back in. If it starts, go find the restriction with the lost suction page before it trips again. If it trips repeatedly with no restriction, the brushes or motor are likely worn.
Step 3: The jumper test at the unit
Unplug the house’s low-voltage wire from the unit’s two terminals. With the unit plugged in, touch a 6 in piece of wire across those two terminals.
If the motor starts, the unit is good. Everything from here on is in the house: the wiring, an inlet, or the hose. Skip to Step 4.
If nothing happens, the fault is inside the unit. Skip to Step 6.
Step 4: Inlets and wiring
Reconnect the house wire at the unit. Open each inlet door and touch the jumper across its two metal contacts. The unit should start at each one.
If one inlet fails and the others work, that inlet has a loose terminal screw on the back of its cover, a chafed or broken wire in its branch, or a bad splice where its wire meets the trunk. Pull the cover (two screws), retighten both terminals, and test again. If it still fails, the break is in the wall or at the splice in the attic or basement.
If every inlet fails but the jumper at the unit works, the break is in the trunk wire between the unit and the first splice. Check the terminals at the unit and the first splice you can reach.
If an inlet starts the unit with the jumper but not with the hose, the inlet’s contacts may be corroded or recessed so the hose end does not touch them. Clean them with a pencil eraser. The low-voltage wiring guide has more on common wiring faults.
Step 5: The hose
Plug the hose into an inlet that passed the jumper test. If the unit does not start, the fault is in the hose: the metal end that bridges the inlet contacts, the two wires running through the hose, or the switch in the handle. If the unit starts when you insert the hose but the handle switch does nothing, it is the switch. Test with a borrowed hose if you can. Switches are replaceable on many hoses; a hose with broken internal wires is replaced. The hoses page explains the types.
Step 6: Inside the unit
If the jumper at the unit does nothing, listen.
A relay click with no motor sound means the control side works and the motor circuit does not: a tripped or failed thermal cutoff, worn-out carbon brushes that no longer touch the commutator, or a dead motor. Brushes are a cheap part and the first thing to check on an older unit. The motor replacement guide covers confirming the motor and reading its label.
A hum or a buzz with no spin means the motor is getting power and cannot turn: a seized bearing or something jammed in the fan. Unplug it immediately.
Silence, no click, means the relay, the circuit board, the transformer, or the cord. On older units the relay is a separate part and inexpensive. On newer units it is on a circuit board. Look for burn marks or a swollen component. The circuit boards and relays page covers matching the part.
Unplug the unit before opening the cover, and keep your hands off the motor’s capacitor if it has one; it can hold a charge after the unit is unplugged.
When to call a pro
Call a licensed electrician for any receptacle or breaker problem, and for any work on the 120V wiring to a direct-connect inlet. Call a central vacuum technician when the fault is inside the unit and you are not comfortable with the circuit board, when the breaker trips every start, when there is a burning smell, or when the unit is under warranty and opening it would void it. A technician’s visit costs a fraction of a new unit and often ends with a relay or a set of brushes.
What to do next
If the jumper sent you into the unit, the motor replacement guide covers brushes and motors. If the unit is old and needs both a motor and a board, compare that to the replacing an old unit guide. If the unit started but keeps tripping off, go to the lost suction page to find the restriction. If it now will not turn off, the runs constantly page is next.
Frequently asked questions
Why did my central vacuum just stop working?
If it stopped while you were using it, the thermal cutoff probably tripped from heat, often because of a clog, a full bin, or a blocked exhaust. Unplug it, let it cool for 20 to 30 minutes, press the reset button if it has one, and try again. If it starts and then trips again, find the restriction before it damages the motor.
How do I test a central vacuum with a jumper wire?
Unplug the house low-voltage wire from the unit's two low-voltage terminals and touch a short piece of wire across those terminals with the unit plugged in. If the motor starts, the unit is fine and the problem is in the house wiring, an inlet, or the hose. If it does not start, the problem is inside the unit. It is a low-voltage circuit and safe to touch.
Why does my central vacuum work at some inlets but not others?
The unit and the trunk wire are good, because some inlets work. The dead inlets have a loose terminal screw, a broken or chafed wire in their branch, or a bad splice where their wire joins the trunk. Open the dead inlet, retighten the terminals, and test with the jumper across its contacts. If that fails, the break is in the wall or at the splice.
Why does my central vacuum work when I plug in the hose but not from the handle switch?
The inlet and wiring are good, because inserting the hose starts it. The hose's internal wires or the switch in the handle have failed. Try another hose if you can borrow one. Handle switches are replaceable on many hoses; otherwise it is a new hose.
Where is the reset button on a central vacuum?
On many units it is a small button on the side or bottom near where the low-voltage wires connect, or near the power cord. Some units reset automatically once the motor cools. Some have no button and rely on the breaker. The manual shows yours. Press it only after the unit has cooled and been unplugged for a while.
When should I call a pro for a central vacuum that will not start?
When the jumper test points inside the unit and you are not comfortable opening it, when the circuit board shows burn marks, when the breaker trips every time the unit starts, or when a motor replacement is needed on a unit still under warranty. Anything involving the 120V wiring to the unit or to a direct-connect inlet is for a licensed electrician.