Prusa error 13608 (FW in Internal Flash Corrupted) appears on the MK4 and its equivalents are #26608 on the MK4S, #21608 on the MK3.9, and #23608 on the MK3.5. The firmware detected that the image stored in the printer’s internal flash memory is corrupted and cannot be trusted to run correctly.

What the Error Means

Firmware corruption in internal flash typically results from a power interruption during a previous firmware update — if the printer lost power while writing new firmware, the flash may contain a partially written image that cannot boot reliably. It can also occur from rare flash memory defects or from an earlier installation of a firmware file that passed signature verification but had internal data corruption. When the bootloader detects a bad CRC or incomplete firmware image, it surfaces this error. The recovery method is straightforward: provide a known-good firmware file on a USB drive so the bootloader can re-flash internal memory.

Step-by-Step Fix

1. Prepare a USB drive with the latest official firmware. On a computer, format a USB drive as FAT32 and copy the correct .bbf firmware file (downloaded from prusa3d.com/drivers for your exact model) to the root directory of the drive.
2. Insert the USB drive into the printer before powering on. Having the firmware file present before power-on gives the bootloader the best chance to detect and use it immediately.
3. Power on the printer. The printer should automatically detect the firmware on USB and begin the recovery flash process. Follow any on-screen prompts.
4. Do not power off during the update process. Wait for the update to complete fully — typically 2–5 minutes. Interrupting the process again risks re-corrupting the flash.
5. Verify the printer boots to the home screen after the update. Confirm the firmware version in Settings → Info matches the file you flashed.
6. Contact Prusa Support if the update fails or the printer cannot boot. If the printer cannot reach the update screen even with a valid USB firmware file, the bootloader itself may be damaged.

Parts Required

• No replacement parts are typically required for this fix — basic tools only
• USB flash drive (FAT32, 32 GB or smaller)

If the USB firmware recovery does not restore normal boot behavior, contact Prusa Support at help.prusa3d.com immediately — do not attempt to power cycle repeatedly, as this can worsen flash degradation.

Frequently asked questions

What does Prusa 13608 mean?

Prusa error 13608 (FW in Internal Flash Corrupted) appears on the MK4 and its equivalents are #26608 on the MK4S, #21608 on the MK3.9, and #23608 on the MK3.5. The firmware detected that the image stored in the printer's internal flash memory is corrupted and cannot be trusted to run correctly.

How do I fix Prusa 13608?

Prusa error 13608 means the internal firmware is corrupted. Learn how to perform a USB recovery flash to restore your MK4-series printer to working condition.