Anycubic error 10121 (Hotbed Heating Abnormal) appears on the Kobra 3, Kobra 3 Combo, Kobra 3 Max, Kobra X, Kobra S1, and Kobra S1 Max when the heated bed fails to reach or maintain its target temperature within the expected timeframe. The printer aborts the job to prevent a thermal safety fault.

What the Error Means

The heated bed relies on a resistive heating mat and an NTC thermistor to form a closed-loop temperature control system. If the thermistor cable is loose or broken, the firmware receives an implausible temperature reading and cannot confirm the bed is heating. If the heating mat itself has failed or its power cable is disconnected, the bed simply will not warm up. A very cold ambient environment (below 10 °C) can also prevent the bed from reaching target temperature quickly enough, triggering the timeout. Finally, a damaged heating output port on the mainboard will produce the same symptom even with good hardware.

Step-by-Step Fix

1. Power off the printer and allow all components to reach room temperature. Locate the heated bed thermistor (NTC) cable — it typically runs along the edge of the bed to a white or black connector at the mainboard. Unplug it and reseat it firmly at both the bed and the mainboard NTC port.
2. Start a small test print or use the preheat menu to command the bed to 60 °C. Watch the temperature reading on the touchscreen — if it rises but slowly, heating is occurring. If the reading stays flat or drops, the heating mat or its power connection is suspect.
3. Power off. With a multimeter set to resistance, measure across the NTC thermistor cable pins. At 25 °C the resistance should be approximately 100 kOhm (±15 kOhm). A reading of 0 Ohm or open-circuit means the thermistor is faulty.
4. With power on and the bed commanded to heat, measure voltage at the mainboard bed-heater output port — it should read approximately 24 V DC during active heating. No voltage here points to a mainboard fault.
5. If the printer is in a cold workshop or garage, move it to a warmer room (above 15 °C) and retry. A thin enclosure or draft shield around the printer can also help retain bed heat during the warm-up phase.
6. If the thermistor resistance is out of range or the heating mat is confirmed cold despite 24 V at the board, replace the heated bed assembly or the NTC thermistor separately if your model supports it.

Parts Required

• Replacement heated bed thermistor / NTC sensor (model-specific)
• Replacement heated bed assembly (if heating mat is failed)
• Multimeter (for thermistor resistance and board voltage checks)

If the bed voltage is correct and the thermistor is within spec but the error persists, contact Anycubic support — the mainboard may require replacement.

Frequently asked questions

What does Anycubic 10121 mean?

Anycubic error 10121 (Hotbed Heating Abnormal) appears on the Kobra 3, Kobra 3 Combo, Kobra 3 Max, Kobra X, Kobra S1, and Kobra S1 Max when the heated bed fails to reach or maintain its target temperature within the expected timeframe. The printer aborts the job to prevent a thermal safety fault.

How do I fix Anycubic 10121?

Anycubic error 10121 means the heated bed is not reaching its target temperature. Fix thermistor cables, heating mat failures, and mainboard issues on Kobra 3 and Kobra S1.