Prusa error 13531 (BBF Allocation Failed) appears on the MK4 and its equivalents are #31531 on the CORE One, #35531 on the CORE One L, #26531 on the MK4S, #27531 on the MK3.9S, #21531 on the MK3.9, #28531 on the MK3.5S, and #23531 on the MK3.5. The firmware could not allocate the memory required to initialize the BBF file system used for storing mesh bed leveling data.

What the Error Means

The BBF (Buddy Board Flash) file system is an abstraction layer the firmware uses to store and retrieve bed leveling mesh data in internal flash storage. When the printer initializes, the firmware attempts to allocate a memory buffer for the BBF operations. If insufficient free memory is available — due to fragmentation from a previously interrupted session — or if the underlying flash storage region is corrupted, the allocation fails. This prevents mesh bed leveling data from loading, which blocks printing on printers that require a valid bed mesh to start a print.

Step-by-Step Fix

1. Restart the printer. A clean restart clears any residual memory fragmentation and is the first thing to try. The allocation often succeeds on a fresh boot.
2. Reset the bed leveling mesh. Navigate to LCD Menu → Calibrations & tests and look for an option to clear or reset the bed leveling mesh. Deleting the existing mesh file forces BBF to create a fresh file, which may succeed where loading a corrupted file failed.
3. Run First Layer Calibration to rebuild the mesh. After resetting, run a new First Layer Calibration to generate a fresh bed leveling mesh and write it to storage.
4. Update firmware. Newer firmware versions include memory allocation improvements and BBF file system fixes. Download from prusa3d.com/drivers and install via USB.
5. Perform a factory reset if allocation continues to fail. Navigate to LCD Menu → Settings → Factory Reset. Note: this clears all calibration data and settings and requires re-setup after the reset.

Parts Required

• No replacement parts are typically required for this fix — basic tools only

If the error persists after a factory reset and firmware update, contact Prusa Support at help.prusa3d.com — the internal flash storage may be failing.

Frequently asked questions

What does Prusa 13531 mean?

Prusa error 13531 (BBF Allocation Failed) appears on the MK4 and its equivalents are #31531 on the CORE One, #35531 on the CORE One L, #26531 on the MK4S, #27531 on the MK3.9S, #21531 on the MK3.9, #28531 on the MK3.5S, and #23531 on the MK3.5. The firmware could not allocate the memory required to initialize the BBF file system used for storing mesh bed leveling data.

How do I fix Prusa 13531?

Prusa error 13531 means memory allocation for the bed leveling file system failed. Learn how to restart, reset bed leveling, and perform a factory reset if needed.