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This page covers fault finding and repair of vacuum cleaners.

Summary

Vacuum cleaners often experience fairly heavy use, and so are one of the commoner domestic appliances to fail. They are fairly low-tech devices and so hold few secrets and aren't usually hard to diagnose or repair.

A problem may simply be due to a failure to regularly empty the dust bag or dust cannister, or to clean or replace filters.

Having checked these, look out for a broken belt or broken plastic parts. However, the latter may be hard to repair as a glued joint will rarely have the strength of the original plastic, though ingenuity and inventiveness or a 3D printer might save the day.

Also, check the motor. Dust in the bearings or the commutator can hopefully be cleaned out and worn brushes can usually be replaced.

The UK consumer rights organisation Which? has a quick overview of simple things to check.

Safety

On opening a vacuum cleaner, live mains may be exposed. Double check that you've unplugged it before you start. It's a good idea to keep the mains plug on the bench in front of you while you work so as to be sure it's unplugged.

Vacuum cleaners (even the hand-held ones) contain powerful electric motors. Keep fingers, loose clothing and children etc. well away from moving parts.

Cordless vacuum cleaners contain rechargeable batteries which can be dangerous if not treated with respect, especially lithium types.

Diagnosis

Bags, filters, blockages and leaks

First of all, check that the problem isn't simply that the bag (or the dust canister for bagless models) isn't full.

Check the filter or filters (there may be more than one) and make sure they're not blocked or in need of replacement. People don't always realize that bagless models also have a filter on the air outlet. This can get blocked, in particular if the dust cannister becomes over-filled. On some models this filter is washable. If after cleaning all the filters it still only sucks weakly, take another look. Sometimes there's yet another filter!

Make sure the bag and filter(s) are correctly fitted.

Check for a blocked hose. If the hose has a blockage, on disconnecting it you should hear the motor slow down markedly.

Check for leaks, for example, a damaged hose. You may be able to temporarily patch up a leaking hose with gaffer tape. On a bagless machine, check for damaged or displaced seals between the dust canister and the machine itself.

Plug, fuse and lead

Check that the plug isn't cracked, the cable grip is gripping the cable, and that the lead is in good condition, with no cracked insulation. If the only damage to the lead is at or close to the mains plug you should be able to cut off the damaged section and reconnect it as a slightly shortened lead. If the cable is self-retracting, the break could be at the other end where it enters the wind-up cable spool. You will need to disassemble it with care, making sure you understand how it works so that you can re-tension the wind-up spring on reassembly.

Open the plug, check the fuse and check that the cable clamp and screw terminals are tight.

Brush

For an upright machine or one with a rotating brush attachment, check the brush. This commonly gets jammed with hairs which get twisted around it. Check the belt which drives it. This may be worn or broken.

As the "business end" of the machine, the surrounding plastic parts take the most punishment. Sometimes a plastic part gets broken, preventing the brush from rotating freely or tensioning the belt.

Disassembly

Any further diagnosis and repair is likely to require disassembly. You will have to inspect the machine to determine which screws are likely to give you the access you need. Sometimes one or more may be security screws requiring a security screwdriver bit, or some of them may be deeply recessed in a hole which is too narrow for the universal screwdriver extension needed to reach the screw. Sometimes you can get purchase on the screw with a small flat screwdriver blade, but you risk damaging the screw and making it impossible to remove even with the correct screwdriver, or damaging the screwdriver blade itself.

Internals

Mechanics

With the machine open check any rubber or nylon drive belts. These are often used to drive the rotating brush on an upright machine. Check they aren't slack and maybe slipping and that bearings aren't jammed with hairs wound round them.

Check whether dust has got into places it shouldn't, maybe because of a badly fitting dust seal or faulty filter, and whether a foreign body has caused any damage. In particular, check the motor. (See later.)

Check for any broken pieces of plastic. These may be causing a purely mechanical problem, or may result in one of the controls failing to actuate a switch or other adjustable electronic component.

Electrical Controls

With the machine open you should be able to use a mutimeter to check electrical continuity from the plug through to the switch and the motor.

The on/off switch may be faulty. Check it with a multimeter on a low resistance or continuity range, that it does indeed read zero (or almost) when on and infinity when off.

In a variable-speed machine there will be an electronic speed control which works in the same way as a dimmer light switch. This isn't easy to test, but look for signs of overheating or burning. If you can temporarily bypass it the motor shold run at full speed. (Make quite sure you're only bypassing the speed controller, and not shorting out the mains!)

The Motor

Review the electric motors page if you're not familiar with how they work.

Check that the bearings aren't clogged with dirt or hairs, and lubricate them. In a bad case you may have to disassemble the motor, generally by removing two bolts running through its length. (If you have to remove the impellor from the motor spindle, bear in mind that the screw which secures it may have a left-handed thread.) Clean the commutator with switch cleaner or isopropyl alcohol on a tissue or cotton wool bud. Check that the motor brushes are free to move up and down in their housings and that the springs are pressing the brushes against the commutator. If they are badly worn the motor may run intermittently or not at all. In a bad case, sparking may have eroded the commutator, perhaps beyond repair.

The motor may have been overheating if it has been labouring or stalled due to excessive dust or a foreign body jamming the impeller. It may also overheat if a blocked air filter impedes the flow of air required to cool it. There may be a thermal cut-out to protect it which should automatically reset when it cools down. However, if the cut-out has been tripping repeatedly or there isn't one, then check for signs of damaged or charred insulation. You may be able to smell the results of overheating if it happened recently and damaged insulation may cause unexplained speed variations. In a bad case overheating may result in the windings burning out, but even if it still seems to work it may no longer be safe to use. Electric motors come in many different shapes and sizes, speeds and power ratings. There are companies that carry vacuum motors, but sometimes their elevated cost makes replacement uneconomic. An alternative might be to cannibalise one from another similar or identical machine.

Cordless vacuum cleaners

Cordless vacuum cleaners work just the same, the only difference being that they have a rechargeable battery and charger or docking station instead of a mains lead.

There is no danger of electric shock, but the motor is still powerful enough to injure your fingers. If shorted, reachargeable batteries can deliver enough current to make a wire hot enough to burn your fingers or even start a fire. Lithium batteries can be very dangerous if physically or electrically abused.

Failure to charge is a common problem. It may be that the battery is dead or that the charger isn't working, and the first thing to do is to determine which. Often a light will be illuminated to indicate that it's charging, but if there isn't one or it doesn't come on a multimeter on a voltage range will show whether the charger is working. If this seems to be the problem, refer to the power supplies page to understand how it works and what might have gone wrong.

Older or cheaper devices use nickel cadmium (NiCd) batteries. For most purposes these days, nickel metal hydride (NiMH) batteries are preferred but NiCd batteries still hold the edge for power tools and remote control cars or boats where the battery must be capable of delivering a heavy current. But the big drawback with NiCd batteries is that they suffer from a memory effect; repeated partial discharge leaves them incapable of delivering a full discharge. In fact, this has been termed the dustbuster effect since it's particularly prevalent in cordless vacuum cleaners only ever used to clear up a few crumbs under the tea table.

Lithium batteries come in a huge range of non-standard and proprietary sizes and you may have to do some hunting to find replacements. However, they also come in a few standard cylindrical forms, such as 18650 (18mm diameter, 65mm in length) which are fairly easy to obtain.

NiCd batteries as used in portable appliances often come in unfamiliar sizes. Whilst unfamiliar in retail outlets, these are still standard industrial sizes and can be found if you search for them. See List of battery sizes for a comprehensive list of sizes which will enable you to determine what it is you're looking for.

A NiCd battery pack often consists of individual cells connected together with spot-welded tags. You can get the required number of individual cells of the tagged variety and solder the tags together, positive to negative, with short lengths of wire. (You cannot solder directly to cells without the spot-welded tags.) Then wrap the whole bundle with PVC tape to keep it together like the original one.

And finally

A vacuum cleaner contains quite a lot of plastic, iron and copper, all of which can be recycled. If you can't repair, recycle.