Prusa error 13828 (Hotend Fan Error) appears on the MK4 and its equivalents are #31828 on the CORE One, #35828 on the CORE One L, #26828 on the MK4S, #27828 on the MK3.9S, #21828 on the MK3.9, and #17828 on the XL. The printer detected that the hotend cooling fan — the fan that cools the heatsink and heatbreak to prevent heat from migrating up into the cold zone — is not spinning at the expected speed.

What the Error Means

The hotend fan runs continuously during printing to maintain the thermal boundary between the hot melt zone (below the heatbreak) and the cold filament feed zone (above it). If this fan stops, heat migrates upward through the heatbreak in a process called heatcreep — the filament softens and jams above the melt zone, creating a blockage that is much harder to clear than a standard nozzle clog. The printer monitors fan RPM via a tachometer and halts immediately when the fan stops to prevent this damage. This is a higher-severity warning than the print fan error (13816) — act on it immediately.

Step-by-Step Fix

1. Power off the printer immediately. Continuing to operate with no hotend fan even briefly risks heatcreep. Turn the printer off as soon as the error appears and do not restart until the fan issue is resolved.
2. Check for debris blocking the fan blades. With the printer off, look at the fan on the side of the Nextruder heatsink. Filament strands or dust can wrap around the blades and stop them. Clear any visible obstruction.
3. Confirm the fan cable is properly connected at the LoveBoard. Remove the Nextruder side cover and check the hotend fan connector on the LoveBoard. Unplug and firmly reseat it.
4. Manually spin the fan blades. Use a toothpick or cotton swab handle to rotate the fan by hand. The blades should turn with very little friction. If the fan is hard to turn or makes a grinding sound, the bearing has failed.
5. Replace the hotend fan if it does not spin freely. A seized bearing will not self-recover. Install a genuine Prusa replacement hotend fan for your Nextruder model.
6. After replacing, power on and confirm the fan spins at startup. Watch for the fan to begin turning within the first few seconds of power-on and verify no error reappears.

Parts Required

• Replacement hotend cooling fan (if fan motor or bearing has failed)
• Compressed air canister (for clearing debris)

If the new fan does not spin after installation, contact Prusa Support at help.prusa3d.com to check the LoveBoard fan output circuit.

Frequently asked questions

What does Prusa 13828 mean?

Prusa error 13828 (Hotend Fan Error) appears on the MK4 and its equivalents are #31828 on the CORE One, #35828 on the CORE One L, #26828 on the MK4S, #27828 on the MK3.9S, #21828 on the MK3.9, and #17828 on the XL. The printer detected that the hotend cooling fan — the fan that cools the heatsink and heatbreak to prevent heat from migrating up into the cold zone — is not spinning at the expected speed.

How do I fix Prusa 13828?

Prusa error 13828 means the hotend cooling fan is not spinning. Learn how to clear obstructions, check the cable, and replace the fan before heatcreep damages the extruder.