Robot vacuum reports 'Error 21' / voice prompt 'Error 21: Filter error' or 'Filter missing' even when a filter is installed.

Safety first: Turn off the robot and remove the dustbin.

• 1. Reseat the filter:
  • Remove the filter from the dustbin.
  • Ensure it is the correct Xiaomi-compatible type.
  • Reinstall it firmly until it locks in place.
• 2. Clean filter and bin:
  • Tap the filter gently to remove dust or replace if very dirty.
  • Clean the dustbin channels and seals.
• 3. Check for obstructions:
  • Inspect the airflow path from the dustbin to the fan inlet for blockages.
• 4. Advanced inspection:
  • Some models use a microswitch or sensor to detect the filter; check its connector and operation.
• 5. Replacement:
  • If the robot still reports filter errors with a new filter, replace the dustbin or the filter detection sensor.