Creality error code 2521 on the K1, K1 Max, and K1C indicates that the strain-gauge leveling sensor chip (HX711 amplifier) is returning a constant fixed value — typically -1 — rather than dynamic pressure readings. The auto-leveling system cannot calibrate the bed without valid sensor data, so any print requiring bed leveling will be blocked.

What the Error Means

The K1-series uses a strain-gauge-based leveling system. The HX711 chip on the leveling sensor board amplifies and digitizes tiny force measurements from the strain gauge as the nozzle contacts the bed surface during probing. When the chip reports a constant value instead of varying measurements, it means the chip has lost its calibration reference, sustained internal damage, or is receiving a bad power or signal connection. Unlike many faults in this range, this error points directly to the sensor chip hardware rather than cable routing — a -1 output is the HX711’s indicator of a communication or power failure.

Step-by-Step Fix

1. Power off the printer before accessing internal boards.
2. Locate the leveling sensor board. On K1-series printers, this board is mounted on the toolhead assembly near the nozzle and connects to the mainboard via a dedicated cable.
3. Unplug the sensor board cable at both ends — at the sensor board and at the mainboard connector. Inspect for loose pins, corrosion, or damaged wiring.
4. Reseat both connectors firmly and ensure the cable is not kinked or under tension.
5. Power on and run the auto-leveling routine. If the sensor board now returns varying values during probing, the connection was the cause.
6. Inspect the sensor board for visible damage — burn marks, cracked components, or obvious physical impact. If damage is visible, replacement is required regardless of cable condition.
7. Replace the Z-axis strain-gauge sensor board if the error recurs after reseating. This board is the field-replaceable unit; the HX711 chip is soldered directly and cannot be swapped independently.
8. Run a full bed-leveling calibration after installing a new sensor board before starting any print.

Parts Required

• Z-axis strain-gauge leveling sensor board (K1 / K1 Max / K1C compatible)
• Phillips-head screwdriver (for toolhead access panels)

Contact Creality support if the replacement sensor board also returns a constant value — the mainboard sensor port may be the underlying fault.

Frequently asked questions

What does Creality 2521 mean?

Creality error code 2521 on the K1, K1 Max, and K1C indicates that the strain-gauge leveling sensor chip (HX711 amplifier) is returning a constant fixed value — typically -1 — rather than dynamic pressure readings. The auto-leveling system cannot calibrate the bed without valid sensor data, so any print requiring bed leveling will be blocked.

How do I fix Creality 2521?

Creality K1/K1 Max/K1C error 2521 flags a failed HX711 strain-gauge chip returning a fixed value. Reseat or replace the leveling sensor board to fix auto-leveling.