21201
Easy Fix
Prusa · FDM 3D Printers
Hotend Fan RPM Too Low - Cooling Fan Underperforming
Quick Answer
Error code 21201 on your Prusa FDM 3D Printers means: Hotend Fan RPM Too Low - Cooling Fan Underperforming. This is usually fixable — see the step-by-step guide below.
Affected Models
Likely Causes
How to Fix It
1
Visually inspect the hotend fan while running to see if it is spinning at full speed
2
Clean the fan blades with compressed air to remove any dust or filament debris
3
Check the fan cable and connector for damage
4
Swap the fan with the part cooling fan temporarily to test if the issue follows the fan or the port
5
Replace the fan if it is noisy, wobbling, or unable to reach full RPM
Pro Tip
This is a common issue that most users can resolve without specialized tools. Try the first step before moving on to more complex solutions.
Parts You May Need
Replacement hotend cooling fan (40mm for MK3S+, Nextruder fan for MK4/MK4S)
Fan cable extension
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