Prusa error 13523 (Loadcell Not Calibrated) appears on the MK4 and its equivalents are #26523 on the MK4S, #21523 on the MK3.9, and #31523 on the CORE One. The firmware detected that the loadcell sensor has not been calibrated since a firmware update or hardware change, and first-layer probing cannot proceed without a valid calibration baseline.

What the Error Means

The loadcell replaces the traditional bed probe on MK4-family printers by detecting the precise moment the nozzle contacts the bed surface through mechanical force. For this to work accurately, the loadcell must first be calibrated to establish a zero-force baseline. After a firmware update, the calibration data may be invalidated if the firmware changes the calibration data format or sensitivity parameters. The same happens after replacing the Nextruder, the nozzle assembly, or the loadcell itself. This error is a blocking notice — printing cannot start until calibration is completed.

Step-by-Step Fix

1. Clean the nozzle before starting calibration. Heat the nozzle to printing temperature, wipe the tip clean with a brass brush or heat-resistant cloth, and allow it to cool. Filament residue on the nozzle tip affects the mechanical contact detection and can cause calibration to produce inaccurate results.
2. Ensure the steel sheet is installed on the bed. Calibration probes the actual print surface — the PEI steel sheet must be flat and seated on the magnetic bed during calibration.
3. Run the loadcell calibration. Navigate to LCD Menu → Calibrations & tests → Loadcell test and follow the on-screen instructions to complete the calibration sequence.
4. Run Full Self-Test first if calibration fails immediately. Navigate to LCD Menu → Calibrations & tests → Self-test to run the full printer self-test, which includes a loadcell check. Resolving any self-test failures first may allow calibration to complete.
5. Contact Prusa Support if calibration cannot be completed. If the calibration routine exits with an error or never reaches the calibration step, the loadcell or its wiring may be the underlying issue.

Parts Required

• No replacement parts are typically required for this fix — basic tools only
• Replacement loadcell sensor (if the sensor is confirmed faulty during self-test — contact Prusa Support)

If calibration fails repeatedly, contact Prusa Support at help.prusa3d.com with the specific error displayed during the loadcell test.

Frequently asked questions

What does Prusa 13523 mean?

Prusa error 13523 (Loadcell Not Calibrated) appears on the MK4 and its equivalents are #26523 on the MK4S, #21523 on the MK3.9, and #31523 on the CORE One. The firmware detected that the loadcell sensor has not been calibrated since a firmware update or hardware change, and first-layer probing cannot proceed without a valid calibration baseline.

How do I fix Prusa 13523?

Prusa error 13523 means the loadcell sensor needs calibration. Learn how to run the loadcell calibration from the menu to restore first-layer probing functionality.