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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 hard to diagnose or repair.

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 contain powerful electric motors. Keep fingers, loose clothing and children etc. well away from moving parts.

Cordless vacuum cleaners contain rechargeable batteries which must be treated with respect, especially lithium types.

Diagnosis

Bags, filters and blockages

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 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 intake. This can get blocked, in particular if the dust cannister becomes over-filled. On some models this filter is washable.

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

Check for a blocked hose. If it has a blockage you should hear the motor slow down markedly when you disconnect it.

Plug, fuse and lead

Check that the plug isn't cracked, the cable grip is gripping the cable, and that lead is in good condition, with no cracked insulation. If any damage to the lead is limited to one end you should be able to cut off the damaged section and reconnect it as a slightly shortened lead.

Open the plug, check the fuse and check 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 be able 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

With the machine open you should be able to use a test meter to check electrical continuity from the plug through to the switch and the motor, though for a multi- or variable-speed machine you will need to trace the wiring and understand how it works.

With the machine open, you should be able to see whether dust has got into places it shouldn't, maybe because of a badly fitting seal or faulty filter. In particular, check 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, and lubricate them. Clean the commutator with switch cleaner or isopropyl alcohol on a tissue. Check that the motor brushes are free to move up and down in their housing and that the springs are pressing them against the commutator.

If the motor has been labouring due to anything that prevents it turning freely, it may have been overheating. 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. This should automatically reset when it cools down, but if the cut-out has been tripping repeatedly or there isn't one, then check for signs of overheating in the motor. In a bad case this may result in the windings burning out, or charring of the insulation leaving it unsafe if it even works at all.

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 test meter 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 not so much for power tools (and remote control cars) 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 as used in portable appliances often come in unfamiliar sizes. Although unfamiliar, these are still standard industrial sizes and can be found if you search for them. See List of battery sizes for a comprehensive list.

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. Then wrap the whole bundle with PVC tape to keep it together like the original one.