- Robot vacuums
- Robot vacuum
Error 21
Roborock Error 21 on robot vacuum: height sensor pressed
Risk level
Low
Usually safe to check without specialist tools.
Urgency
Low
Quick answer
Roborock shows Error 21: the height sensor has been pressed or is stuck. Move the main unit to a new location and restart it; if it repeats, check under low furniture where the robot stopped and look for anything jammed around the sensor.
Safety first
Stop and check this first
- Do not carry the robot by the laser scanner cap, the main unit cover or the bumper, and do not pry at the sensor. The manual warns against carrying it that way.
Safe checks you can perform
- Move to a new location
- Check around the height sensor
- Reset the system
Leave these tasks to a qualified professional
- Do not attempt this professional task: Height sensor test by authorized service
- Do not attempt this professional task: Case review by Roborock after-sales
What a technician must be able to justify
A technician is coming
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Height sensor test by authorized service
What they doRoborock's authorized service tests the height sensor and its mechanism with the robot opened and powered off.
They must show youthe sensor reading pressed with nothing touching it.
In writingwhether the sensor was replaced and its reference.
Case review by Roborock after-sales
What they doRoborock after-sales service reviews the case after you have done the manual's steps and a system reset.
They must show youthe case number and their diagnosis.
In writingwhether the repair is covered by warranty and what is replaced.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Checks and evidence, step by step
Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
- 1
Move to a new location
No special tools
Procedure
- Who:
- you.
- How:
- move the main unit to a new location in open space and restart it, as the manual says.
- Result that matters:
- whether it runs without Error 21.
- If it runs:
- the spot where it stopped was pressing the sensor; block that area with a no-go zone.
- If it repeats in open space:
- check around the sensor.
- Evidence to keep:
- a photo of where it stopped.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
- 2
Check around the height sensor
No special tools
Procedure
- Who:
- you, with the robot switched off.
- How:
- look around the height sensor shown in the manual's diagram for anything caught or holding it down, and remove only loose debris without prying.
- Result that matters:
- that nothing is pressing on the sensor.
- If debris was holding it:
- remove it and test again.
- If nothing is there:
- reset the system.
- Evidence to keep:
- a photo of the area around the sensor.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
- 3
Reset the system
No special tools
Procedure
- Who:
- you.
- How:
- press the Reset button (under the top cover) to restart the main unit. The manual warns this also resets scheduled cleaning, WIFI and related settings.
- Result that matters:
- whether the error is gone after the restart.
- If it is gone:
- the reset cleared it; set your schedule and WIFI again.
- If it persists:
- the manual suggests restoring factory defaults, then contacting after-sales.
- Evidence to keep:
- a note of the reset time and the result.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- Robot vacuums
- Brand
- Roborock
- Product type
- Robot vacuum
Known code variants
- 21
- error 21
- Error 21 height sensor
- Height sensor has been pressed
- iPhone error 21
- iTunes error 21
- Mi Electric Scooter error 21
- Ninebot codigo 21
- Ninebot error 21
- patinete Segway error 21
- patinete Xiaomi error 21
- Roborock Error 21
- Segway error 21
- Segway Ninebot E2 Pro error 21
- Segway Ninebot error code 21
- Xiaomi bateria error 21
- Xiaomi error 21
- Xiaomi error 21 6 km/h
- Xiaomi scooter error 21
What it means
In the Roborock S6 manual, Error 21 means the height sensor has been pressed or is stuck, and the fix is to move the main unit to a new location and restart. The height sensor appears in the manual's sensor diagram; it tells the robot when something presses on it, so the spot where the robot stopped, such as low furniture, can trigger it. The code does not prove the sensor is broken: the manual's step is to move the robot, and only a repeat in open space after a reset points to service.
Warnings and stop conditions
- Lowsource verified
Do not carry the robot by the laser scanner cap, the main unit cover or the bumper, and do not pry at the sensor. The manual warns against carrying it that way.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
Symptoms and causes
Probable causes · in order
- Wedged under low furnitureCommon
The robot stopped under a sofa, bed or cabinet with little clearance and restarts normally in open space.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
- Sensor held down by debrisPossible
It repeats in open areas and something is caught around the sensor that keeps it pressed.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
- Sensor stuckLess common
Nothing is pressing it, it repeats in open space and after a system reset, so service should test it.
Evidence: Roborock S6 Robotic Vacuum Cleaner Manual
Virtual technician
Does Error 21 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Roborock S6 Robotic Vacuum Cleaner Manual
Roborock · 2026 · official_doc
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