HMS 0300-0200-0001-0003: nozzle heater over temperature
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The nozzle heater ran hotter than the firmware allows and the printer shut it down. This is a protective stop working correctly. Find out why the temperature ran away before you print again.
Bambu reports the right extruder nozzle temperature as abnormal with the heater over temperature. The firmware compares the requested temperature against the thermistor reading, and when the reading climbs past the ceiling it cuts power.
Affected machines: A2L, H2, H2C, H2S, P2S, X1 series.
This is a thermal protection event. Do not disable it, do not raise the temperature ceiling, and do not run the machine unattended until you know the cause. A heater stuck on with no protection is how printers start fires.
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Two failure modes produce the same code
The heater is stuck on. A shorted MOSFET on the control board keeps supplying power regardless of what the firmware asks. The tell is temperature that keeps climbing after the print is cancelled. This needs a board, not a nozzle.
The thermistor is lying. A sensor that has drifted or lost contact reads low, so the firmware keeps heating to compensate, and the real temperature overshoots until a second check catches it. The tell is a reading that jumps around during warm-up.
Print aborts with an over-temperature error on the nozzle
Either the heater cannot be switched off, or the temperature reading is wrong
- Power off and let the hotend cool completely. Do not retry immediately.
- Watch a cold warm-up from the machine display. A healthy hotend climbs smoothly; a faulty thermistor produces jumps and dips.
- Cancel mid-warm-up and watch the reading. It should fall. If it keeps rising, the heater is stuck on — stop and contact support.
- If warm-up is erratic, reseat the thermistor connector at the toolhead.
- Check for purged plastic packed around the heater block. A blob of insulation traps heat and skews the reading.
What not to do
There is a well-travelled piece of advice online about editing firmware limits to make temperature errors go away. On a machine with a stuck heater that advice removes the only thing standing between a fault and a fire. If the error repeats after the checks above, the machine needs a part replaced.
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