Why has my blender stopped working or started smelling hot?

Blenders have three protections and one common wear part, and between them they account for nearly every failure. The symptoms are distinguishable in seconds: silence, a stop after running, or a running motor with still blades. Only one of the four means the appliance is finished.

Safety

Step by step

1. Unplug it, then work out which of the four symptoms you have.Silent with no motor noise; stopped mid-blend with a hot smell; motor running with the blades not turning; or leaking rather than failing. Each has a different cause and they do not overlap.
2. For silence, check the interlock first.Nearly every jug blender has a switch that only closes when the jug is twisted fully onto the base and, on many, when the lid is locked too. A jug placed on rather than turned into its lock gives a completely dead machine. Take it off and refit it deliberately.
3. Check the seating surfaces are clean.Dried smoothie in the locking ring or on the base pad stops the jug seating far enough to make the interlock. Wipe both and try again — this is a surprisingly common cause of a blender that has 'died' after a messy session.
4. For a stop mid-blend with a hot smell, wait.That is the thermal cut-out, which trips when the motor overheats, usually from a thick mixture with too little liquid or a long continuous run. Unplug it, let it stand 20 to 30 minutes, and it will normally reset itself. Then blend in smaller batches with more liquid.
5. For a running motor and still blades, look at the coupling.A plastic drive coupling links the motor spindle to the blade assembly and is designed as the sacrificial part. Stripped splines mean the motor spins freely. On many models it is a cheap replaceable part; on cheaper ones it is moulded in and the appliance is finished.
6. For leaking, check the blade assembly seal.Jugs that unscrew from their blade assembly have a rubber gasket that perishes and gets displaced during washing. Take it apart, check the gasket is present, undamaged and correctly seated, and reassemble hand tight.
7. Check the jug and blade bearing for roughness.Unplugged, turn the blade assembly by hand. It should spin freely with a little resistance and no grinding. A rough or seized bearing is what causes overheating in the first place, and it is not repairable on domestic machines.
8. Decide whether it is worth going further.Interlock, cleaning, thermal reset and a gasket are all yours. A coupling is often a cheap part worth ordering. A failed motor or a seized bearing on a mid-range blender is the end of the appliance, because the motor is the majority of its cost.

Tips

• Add liquid first, then solids. Most thermal cut-outs are caused by a packed jug with nothing to circulate.
• Work in short pulses rather than long continuous runs for thick mixtures. It moves the contents back onto the blades and gives the motor time to shed heat.
• Wash the seating ring on the base as well as the jug. Residue there is the cause of half the interlock complaints.
• If the blender is under warranty, do not take the base apart. Interlocks and thermal cut-outs are entirely diagnosable from outside and opening it will void the cover.

Common mistakes

• Defeating the lid or jug interlock — It is the only thing preventing the blades running with the jug off or the lid open. There is no version of this that is a sensible trade.
• Running a thick mixture continuously — The blades cavitate in a pocket of air while the motor works against a stalled load, which is exactly how the thermal cut-out gets tripped and the coupling stripped.
• Assuming a hot smell after a cut-out means a dead motor — The cut-out exists to prevent that. Give it half an hour unplugged before concluding anything — most blenders come back perfectly.

If it doesn't work