Prusa error 13816 (Print Fan Error) appears on the MK4 and its equivalents are #31816 on the CORE One, #26816 on the MK4S, #27816 on the MK3.9S, #21816 on the MK3.9, and #17816 on the XL. The printer detected that the print cooling fan — the fan responsible for cooling the extruded filament and overhangs — is not spinning within the expected RPM range.

What the Error Means

The print fan (also called the part cooling fan) blows air directly onto the freshly deposited filament to solidify it quickly, which is essential for printing overhangs, bridges, and fine details. The Buddy board monitors fan speed via a tachometer signal. When the measured RPM falls below the expected threshold — because the fan blades are blocked, the cable is disconnected, or the fan motor has failed — the printer raises this error. Running without adequate part cooling causes stringing, poor overhangs, and potential heat-related deformation of the printed part.

Step-by-Step Fix

1. Check for visible debris blocking the fan blades. Look into the fan shroud from the front of the print head. Filament threads, dust bunnies, and small debris are common culprits. Power off before touching the fan.
2. Use compressed air to clean the fan. A short burst of compressed air from a can will dislodge most debris without risking damage to the blades.
3. Confirm the fan wire is connected at the LoveBoard or print head connector. The print fan cable connects to the LoveBoard inside the Nextruder. With the printer off, access the LoveBoard by removing the Nextruder side cover and check that the fan connector is fully seated.
4. Manually spin the fan to test blade freedom. With the printer off, use a toothpick or cotton swab handle to gently spin the fan blades. They should rotate freely with very little resistance. A fan that requires force to spin has a seized bearing.
5. Replace the print fan if it does not spin after clearing obstructions. A fan with a seized bearing or failed motor will not recover on its own. Install a replacement part cooling fan matched to your Nextruder model.

Parts Required

• Replacement part cooling fan (if the fan motor has failed or bearing is seized)
• Compressed air canister (for cleaning)

If the fan is replaced but the error persists, contact Prusa Support at help.prusa3d.com — the LoveBoard fan output circuit may need evaluation.

Frequently asked questions

What does Prusa 13816 mean?

Prusa error 13816 (Print Fan Error) appears on the MK4 and its equivalents are #31816 on the CORE One, #26816 on the MK4S, #27816 on the MK3.9S, #21816 on the MK3.9, and #17816 on the XL. The printer detected that the print cooling fan — the fan responsible for cooling the extruded filament and overhangs — is not spinning within the expected RPM range.

How do I fix Prusa 13816?

Prusa error 13816 means the part cooling fan is not spinning as expected. Learn how to clear obstructions, check the cable, and replace the fan if needed.