Kobra S1 or Kobra 3: errors 10121, 10122, 10123 or 10124 (bed or printhead not heating, or thermistor fault)

Symptom

The Kobra S1 or Kobra 3 stops with 10121 (hotbed heating abnormal), 10122 (extruder heating abnormal), 10123 (hotbed NTC abnormal) or 10124 (extruder NTC abnormal). The printer cuts heating to protect itself and will not continue.

Likely causes, from most to least likely

1. 10121: the bed cable is loose or detached at the mainboard, or the heated bed is faulty.
2. 10122: the hotend heater cable is loose or not fully inserted, the heater has failed, or the printhead board has failed.
3. 10123 (Kobra 3): the bed thermistor (T1) cable is loose at the mainboard, or the room is below 10 °C.
4. 10124: the printhead thermistor cable or the printhead connection cable is loose, or the thermistor is damaged.

Checks to tell which one it is

• With the printer cold, look at the temperature on screen: it should be close to room temperature (about 25 °C). If the room is below 10 °C, 10123 can appear.
• 10121: set the bed to 50 °C and watch the blue light on the mainboard: on means heating; flashing means target reached; off means the bed is not heating.
• 10122 on the Kobra S1: with the printhead rear cover removed, set the nozzle to 55 °C and watch the printhead board light: solid means heating; flashing means target reached; off means a board fault.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Switch off and let it cool

   Before touching any cable, switch the printer off, unplug it and wait until the hotend and bed are cold. Always hold connectors by the body, never pull the wires.

   Check: The printer is disconnected and cold.

   If that does not fix it: Do not continue if you cannot disconnect it.

2. Printhead (10122 and 10124): reseat the cables

   Remove the printhead front cover and disconnect the fan. Reseat the hotend heater cable (10122) or the thermistor cable (10124), and also the printhead connection cable on its adapter board. When refitting the hotend, make sure it is fully seated.

   Check: On the Kobra 3, Anycubic suggests heating the printhead to 210 °C for 10 minutes: if the error does not return, you can print.

   If that does not fix it: If 10122 persists, the hotend or printhead board may be faulty: contact Anycubic support.

3. Bed (10121 and 10123): check the wiring at the mainboard

   Kobra S1: unplug the signal cable at the rear cover, remove the four-input one-output module and the rear cover (2.0 mm key) and check that the bed cable is held firmly on its adapter board. Kobra 3: remove the bottom cover (2.5 mm key) and check the bed cable and the T1 thermistor cable on the mainboard; reseat and tighten them if loose.

   Check: The bed heats to 50 °C with the blue light on and no error.

   If that does not fix it: On the Kobra S1, if the light does not come on while heating, Anycubic says to replace the heated bed.

4. If it is cold (10123)

   If the room is below 10 °C, move the printer somewhere warmer and let it warm up before switching it on.

   Check: The idle temperature reads normally and the warning disappears.

   If that does not fix it: Check the T1 cable (step 3).

5. Multimeter checks (only with electrical knowledge)

   Anycubic describes multimeter checks: the Kobra 3 bed thermistor should read about 100 kΩ (±10) at 25 °C with the printer off, and other voltage checks are done with the printer powered on. If you are not experienced, do not do them: contact Anycubic support.

   Check: You know whether the bed, the cable or the mainboard is at fault.

   If that does not fix it: Contact support with a screenshot of the error, the serial number and the firmware version.

Prevention

• Do not pull on the thermistor wires when changing the nozzle or force the hotend when clearing a clog.
• When refitting the hotend, check that its cables are not pinched.
• Use the printer in a room above 10 °C.

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Printers it applies to

Anycubic Kobra S1 and Kobra 3.

Official sources

This guide summarises the official documentation linked here:

• Kobra S1 - CODE: 10121 Heat bed heating abnormality · Anycubic
• Kobra 3 Combo - CODE: 10121 Hotbed heating abnormally · Anycubic
• Kobra S1 CODE: 10122 Extruder heating abnormally · Anycubic
• Kobra 3 CODE: 10122 Extruder heating abnormally · Anycubic
• Kobra 3 CODE: 10123 Hotbed NTC abnormal · Anycubic
• Kobra S1 - CODE: 10124 Extruder NTC abnormal · Anycubic