| Loses suction or pulses | - Clogged filter
- Blockage in wand, head or inlet
- Full bag or bin
- Split hose
- Worn seal
- Failing suction motor
| - Test suction at the head, then at the wand, then at the body.
- Look through the wand and into every inlet with a torch.
- Check the bin or bag is not full and the filters are not caked.
- Bagged machines: flex the hose and listen for a whistle from a split.
| - Video of the machine running with your hand over the inlet.
- When filters were last washed or replaced.
- Whether it pulses or cuts out.
| Basic to Advanced, depending on the cause Diagnosis time: Under an hour Low safety relevance | Clearing a blockage costs nothing. Genuine filters, a hose or seals are moderate parts. A failing motor is not an economic repair on most used machines. | - Weak suction at the body with clean filters.
- Motor noise that rises and falls or screams.
- Signs that the machine has sucked up liquid or fine building dust.
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| Brush bar not spinning | - Hair or thread wound round the brush
- Worn brush bearing or end cap
- Broken drive belt
- Cleaner-head motor or wand contacts
| - Remove the brush bar the way the manual shows and cut away hair and thread.
- Spin it by hand: smooth, or gritty and stiff at the ends?
- Check the electrical contacts between head, wand and body for dirt or damage.
| - Whether the head has ever worked on this body.
- Exact head model.
| Basic to Advanced, depending on the cause Diagnosis time: Under an hour Low safety relevance | Cleaning is free. A brush bar or end cap is a modest part. If the head’s own motor has failed, the fix is a replacement head, which can be a large share of the machine’s value. | - Brush is free and clean but still does not turn.
- Melted plastic around the brush ends.
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| Runs briefly, cuts out or will not charge | - Worn-out battery
- Wrong or faulty charger
- Blockage in wand, head or inlet
- Trigger or electronics fault
| - Rule out a blockage first — some cordless machines cut out or pulse when airflow is restricted.
- Check the charger is the right one and what the indicator lights show.
- Look at the battery case for swelling, cracks or heat marks.
| - Battery age and whether it is genuine.
- Runtime on the normal setting, timed.
| Basic to Advanced, depending on the cause Diagnosis time: Under an hour Safety-relevant | A genuine battery is a significant cost on older models, and some are screwed in rather than click-in. Non-genuine batteries are a safety and resale risk. | - Swollen or damaged battery.
- Third-party battery of unknown origin.
- Cuts out with a clear airway and a good battery.
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| Burning smell, loud motor or overheating | - Failing suction motor
- Electrical damage
- Cleaner-head motor or wand contacts
| - Switch off and unplug. Look only: scorch marks, melted plastic, smell.
| - What happened just before — liquid, a jammed brush, a long run on a blocked filter.
| Advanced to Professional, depending on the cause Diagnosis time: Under an hour Safety-critical | Motor, wiring and board faults are not maintenance. On mains machines they are also an electric-shock and fire risk. | - Always, unless you are buying it for accessories at accessory prices.
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| Robot will not charge or dock | - Dirty charging contacts
- Worn-out battery
- Dock or power-supply fault
- Corrosion from liquid
| - Clean the charging contacts on robot and dock with a dry cloth and try again.
- Check the dock’s power supply is the original and its light is on.
- Look inside the bin bay and under the robot for corrosion or dried liquid.
| - Battery age and whether it is genuine.
- The exact error message or light pattern.
| Basic to Advanced, depending on the cause Diagnosis time: Under an hour Safety-relevant | Contacts cost nothing to clean. A genuine battery is a moderate part. Corrosion or a charging-circuit fault usually ends the project. | - Any corrosion.
- Non-genuine battery with a charging error.
- Robot was used on wet floors it was not built for.
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| Robot navigation, bumper or wheel errors | - Dirty sensors
- Jammed wheel module
- Still paired to the previous owner
| - Wipe cliff, wall and dock sensors and the camera or lidar window.
- Press each wheel in: it should spring back and turn freely.
- Press the bumper at several points: it should click and return.
- Ask the seller to factory-reset it and remove it from their account.
| - Error number or message.
- Whether it completes a room and returns to the dock.
| Basic to Advanced, depending on the cause Diagnosis time: Under an hour Low safety relevance | Brushes, filters and side brushes are consumables. Wheel modules are replaceable on some models. Navigation hardware faults are not worth chasing. | - Still tied to the previous owner’s account.
- Navigation errors after sensors are clean.
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