HMS 0300-0100-0001-0003: heatbed over temperature
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HMS 0300-0100-0001-0003 means the heated bed went past its temperature limit and the protection cut the heater. Something told the controller to keep heating when it should have stopped. That something is usually a temperature sensor reading lower than the truth, and finding it matters more than clearing the code.
Affected machines: X1 series. An over-temperature event on a bed is not like one on a hotend. The bed is large, it holds heat, and it is the mains load in the machine, so the firmware treats crossing the limit as a hard stop rather than a warning.
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Three things drive a bed past its limit
A sensor reading low. The most common by far. If the thermistor reports 60 degC when the bed is at 90, the controller keeps heating and the protection is the only thing that notices. Measure it cold: around 100k ohm is healthy on these machines.
A control circuit stuck on. Less common and more serious, because it means the heater keeps receiving power regardless of what the controller asks. That is a service fault.
Trapped heat. Something under or on the plate holding heat in one spot, or a plate that is not sitting flat so that a hot region cannot spread. This is the one cause you can see and fix yourself.
Bed heating stops and the printer reports the heatbed is over temperature
Temperature sensor reading low, a stuck control circuit, or trapped heat under the plate
- Unplug the printer at the wall and let the bed cool completely before touching it.
- Lift the build plate and check underneath for anything trapped between the sheet and the bed.
- Check that the plate sits flat and fully seated against its locating features.
- Measure the bed thermistor cold. Around 100k ohm is healthy; a reading well below that explains the overheat.
- Inspect the bed cable for a pinch or chafe that could short the sensor low.
- Do not clear the code and print. If the sensor measures healthy, the control side is at fault and that is a service item.
Take the temperature reading seriously as evidence. A sensor that reads low is a cheap, findable cause with a clear story behind it, and it is worth measuring before accepting the more expensive explanation.
The open-circuit version is heatbed heater open circuit, and the sensor fault is heatbed sensor short circuit. Our page on bed temperature explains the control loop, and the troubleshooting index covers the rest.
HMS 0300-0100-0001-0003 FAQ
Can I clear the code and try again?
No. The protection stopped a runaway heater. Running it again without finding the cause repeats the event.
What should the bed sensor read?
Around 100k ohm at room temperature, falling as it warms.
Could the build plate cause this?
A plate that does not sit flat, or something trapped underneath it, can create a hot spot. It is worth checking first because it costs nothing.
Is the bed damaged?
Usually not. The protection exists to stop the event before damage, which is why it fired.
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