The most common reason a power tool starts to smell of burning or give off smoke is worn carbon brushes arcing inside the motor. It isn't the only reason, though.
An overheating motor, a dry bearing, a slipping belt, or a failing battery on a cordless tool can all produce a burning smell or smoke, and they don't all mean the same thing.
Some are a five-minute job that costs a few pounds. Others mean you should stop using the tool straight away. This guide explains what each smell and each colour of smoke is telling you, how to narrow down the cause, how to fix the ones you safely can, and when to stop and get the tool looked at.
Is it safe to keep using a power tool that smells of burning or smokes?
Usually, no. If you can see smoke, switch the tool off, unplug it or take the battery out, and find the cause before you use it again. A faint, brief smell you can investigate once the tool has cooled. Visible smoke or a strong smell is a stop sign.
Stop straight away, and don't restart the tool, if you notice any of these:
- Flames, or smoke that keeps coming after you ease off
- A hot, melting-plastic smell from the cable, plug or trigger switch (that points to an electrical fault, not a worn part)
- A cable or plug that feels hot, or shows scorch marks
- The tool tripping your RCD or breaker for no obvious reason
A hot-plastic or burning smell, scorch marks and tripped breakers are recognised electrical-fire warning signs, according to West Sussex Fire and Rescue, so treat them seriously rather than working through them. Don't breathe the fumes from burning plastic or insulation either. Work somewhere ventilated, and keep children and pets out of the way.
What do the different burning smells and smoke colours actually mean?
The smell, and the colour of any smoke, is the fastest clue to what has gone wrong. Before you take anything apart, take note of what you are actually smelling.
- Sharp, electrical, ozone-like smell (a bit like the air after a thunderstorm): usually sparking carbon brushes, or arcing at the commutator (the copper segments the brushes press against). It often comes with visible sparking through the vents.
- Hot plastic or varnish smell: usually an overheating or burnt motor winding, where the insulation on the copper wire is cooking. This one is more serious.
- Burning rubber: usually a slipping or perished drive belt on belt-driven tools like belt sanders.
- Hot oil or grease: usually a dry bearing or gearbox.
Smoke colour helps too. Thin blue or white smoke from the motor housing tends to point to the brushes or windings, while smoke or a scorched smell from around the cable or switch points to an electrical fault.
We will go through each cause below, starting with the most common.
If yours is the sharp, sparking kind, there is more detail in our guide on how to stop motor brushes from sparking.
Is it the carbon brushes? (the most common cause)
In most power tools, the answer is yes. Drills, angle grinders, circular saws and sanders run on brushed motors, and inside them two small blocks of carbon, the carbon brushes, press against the spinning commutator to pass current to the motor. They are designed to wear down gradually, so the wear falls on a cheap, replaceable part rather than on the motor itself.
As a brush wears too short, the contact gets patchy and it starts to arc and spark. That is what produces the sharp smell, and the sparking you can see through the air vents. We make our own carbon brushes, so this is the failure we see more than any other: most "dead" tools people ask us about just need a fresh set of brushes.
The signs that point to the brushes:
- Heavy or increasing sparking through the vents
- The tool cutting out or losing power intermittently
- A sharp, electrical burning smell rather than a hot-plastic one
One thing matters more than anything else here: brushes are model-specific. There is no universal carbon brush. A Dewalt Type 3 and a Type 4 of the same drill can take different brushes, and the Evolution RAGE 3 and RAGE 3S look almost identical but don't share a brush. Fit the wrong brush and it may not run properly. Worse, it can damage the tool.
If you are not certain which you need, our guide to finding your tool's model number shows you where to look.
If worn brushes turn out to be the cause, a matched set from our replacement carbon brush range is usually all it takes to get the tool running again.
Could the motor be overheating from overload or blocked vents?
Yes, and this is the next most common cause after the brushes. Push a tool too hard, run it too long, or work with a blunt blade or bit, and the motor has to strain, runs hot, and gives off a hot, slightly varnishy smell. Dust packed into the cooling vents does the same thing by trapping the heat inside.
If the tool has just been working hard, stop and let it cool fully before you do anything else. A one-off overheat from a heavy job often clears once the tool is cool and you ease off the pace or fit a sharp blade. If it overheats again on a normal load, there is a deeper fault.
Clogged vents are worth checking every time. Blow the dust out of the air vents with compressed air, and keep your hands clear of the exhaust vents where the hot air comes out.
When is it a burnt-out motor, the windings or armature?
A persistent hot-plastic smell with visible smoke usually means the motor itself is failing, specifically the windings (the coils of insulated copper wire) or the armature (the rotating part the brushes feed). When the thin insulation on that wire breaks down or shorts, it burns and smokes. This is the most serious cause, and the least DIY-friendly.
A burnt-out motor often follows months of ignored sparking or repeated overheating, which is exactly why we push people to act on worn brushes early. Once the damage is in the armature, you are usually looking at a professional repair or a new tool rather than a few-pound part. More on that decision below.
Could it be the bearings, gears or a slipping belt?
Mechanical parts smell hot too, and they each smell slightly different. A dry or failing bearing gives off a hot-metal or burning-grease smell, often with a grinding or rumbling noise. A dry gearbox smells of hot grease. A slipping or perished drive belt, on belt sanders and some bench tools, smells of burning rubber.
The giveaway with mechanical faults is that you usually hear or feel something as well as smell it: a grinding, a squeal, or the tool feeling rough or binding rather than spinning freely. A worn drive belt is one of the cheaper and easier mechanical fixes, so it is worth checking early on any belt-driven tool.
Is a burning smell from a brand-new power tool normal?
Often, yes. A faint smell the first few times you run a new tool is usually the protective varnish on the motor windings, and the fresh carbon brushes bedding in against the commutator. It should fade within the first few uses, and is nothing to worry about.
What is not normal on a new tool is visible smoke, a strong or worsening smell, or heavy sparking. That points to a fault rather than break-in, and on a tool still under warranty it is worth returning rather than opening up.
What if it's a cordless tool, could the battery be the problem?
On a cordless tool, work out whether the smell is coming from the motor or the battery, because they are very different problems. A chemical or hot smell, swelling, or heat coming from the battery pack itself is the serious one. Stop using it, stop charging it, and move the pack somewhere away from anything flammable.
A damaged or faulty lithium-ion cell can overheat and tip into thermal runaway, a self-feeding reaction that can end in fire, which is why a suspect battery or charger should be taken out of use rather than nursed along. Stick to the manufacturer's own batteries and chargers, as cheap unbranded ones are a known cause. A UK government safety report on a faulty power-tool battery describes exactly this: a short inside the pack leading to overheating, thermal runaway and fire.
If the smell is clearly coming from the motor rather than the battery, the brush and overheating checks above all apply, and changing the brushes in a cordless drill is a straightforward job.
How do you fix a power tool that smells of burning or smokes?
Once you know the cause, the fix usually follows. The common ones are well within reach of a confident DIY-er; the electrical ones are not. Work safely: always unplug the tool or remove the battery first, and let it cool.
- Worn brushes: remove the brush caps (the screw covers on the motor housing) and check the carbon. If it is worn short, chipped, or past the wear line, replace both brushes as a matched pair. Never fit just one.
- Blocked vents or overheating: blow out the cooling vents and give the tool a rest. Ease off the workload, and sharpen or replace blunt blades and bits.
- Slipping belt: on a belt-driven tool, fit a new drive belt.
- Burnt motor, or any electrical smell from the cable or switch: stop. This is a job for a professional repairer, or a sign it is time to replace the tool.
While you have the brushes out, check the springs and brush holders too. A spring that has lost its tension or gone discoloured won't hold the new brush against the commutator properly. There is a full walkthrough in our guide on how to change carbon brushes in power tools. Once you have fixed it, run the tool briefly with no load to check the smell and the sparking have gone.
Should you repair the tool or replace it?
It comes down to the cause, and what the tool is worth. A worn brush set is a cheap fix, usually a few pounds, and well worth doing on any tool you would miss. A burnt-out motor or an internal electrical fault is a different matter: on an inexpensive tool, the repair can cost more than a replacement.
This is why it pays to act early. Worn brushes left in place too long stop being a few-pound job and start arcing into the commutator and armature, which is a far more expensive repair, if a part is even available for an older tool. Catch them while they are just worn, and the maths is simple.
Our guide on how long carbon brushes last gives you a rough idea of when to expect to change them.
How do you stop it happening again?
Most burning-smell problems are avoidable with a bit of routine care:
- Don't force the tool, and keep blades and bits sharp so the motor isn't straining
- Let it cool between heavy runs rather than working it flat out
- Keep the cooling vents clear of dust, and use dust extraction where you can
- Check the brushes for wear as part of normal maintenance, before they start sparking
- Store tools somewhere dry
A few minutes of this saves most of the failures we see. There is more in our guide on how to maintain your power tools.
Is a burning electrical smell toxic or harmful to breathe?
The fumes from burning plastic, motor insulation or a hot motor are unpleasant and can irritate your eyes, nose and throat, so don't sit there breathing them in. Open a window or work outside, and stop using the tool until you have found the cause.
A brief whiff while you switch the tool off is unlikely to do a healthy adult any harm. Persistent smoke from melting insulation is a different matter, and should be treated as a fire risk rather than just a bad smell, so keep children and pets away and don't leave the tool running.
The short version: a sharp, electrical smell with sparking is almost always the carbon brushes, and that is a cheap fix; a hot-plastic smell with smoke is more likely the motor and needs more care; and anything coming from the cable, switch or a cordless battery means stop now.
Work out which smell you have got, deal with the simple causes, and don't keep running a tool that is telling you something is wrong.