MINTEMP and MAXTEMP errors: how to fix thermistor faults on a 3D printer

A MINTEMP error means your printer's temperature sensor is reading impossibly cold; MAXTEMP means it's reading dangerously hot. In stock Marlin the limits are 5 °C for MINTEMP and 275 °C (hotend) or 150 °C (bed) for MAXTEMP. MINTEMP is almost always an open thermistor circuit, and MAXTEMP is usually a short. Either way the firmware cuts every heater and halts until you fix the wiring and reset.

What MINTEMP and MAXTEMP errors mean

Most hotends and beds use a 100k NTC thermistor. Its resistance falls as it heats up, and the firmware converts that resistance into a temperature. When the circuit breaks, resistance goes to "infinite" and the firmware sees an impossibly cold reading: MINTEMP. When the two legs touch (a short), resistance drops to almost zero and the firmware sees an impossibly hot reading: MAXTEMP.

So neither error usually means the printer is actually cold or hot. It means the firmware can no longer trust its sensor, and a heater it can't measure is a fire risk, so it switches everything off.

• MINTEMP in Marlin only trips while that heater has a target temperature, which is why it often appears the moment you preheat or start a print.
• MAXTEMP trips at any time, even with the heaters off.
• Both are a hard stop. Marlin shows PRINTER HALTED and Please Reset; Klipper reports a shutdown and needs FIRMWARE_RESTART.

MINTEMP and MAXTEMP messages by printer and firmware

Every firmware words the same fault differently. Find yours here, then use the diagnosis steps below, which are the same for all of them.

For every other code on these printers, use the 3D printer error code lookup.

How to diagnose a thermistor fault, step by step

Work through these in order. Most people find the fault by step 3. Tick them off as you go.

1. Read both temperatures cold. With the printer at rest, hotend and bed should show within a few degrees of room temperature. On Marlin you can send M105 from a terminal; on Klipper, watch the temperature graph in Mainsail or Fluidd. One sensor far below room temperature suggests an open circuit; one reading hundreds of degrees cold suggests a short.
2. Do the wiggle test. Gently flex the thermistor wires where they leave the heater block, at the toolhead connector and where the cable bends in the chain. If the reading spikes or drops out, you've found a broken conductor or a bad crimp.
3. Do the warm-air test. Blow warm air from a hair dryer at the thermistor and watch the screen. The reading should climb smoothly. No change at all means a dead thermistor or broken wire (Prusa's support team uses this exact test).
4. Swap ports to rule out the mainboard. With the power off, swap the hotend and bed thermistor plugs at the board if they use the same connector and sensor type. Power on without heating. If the bad reading moves with the cable, the sensor or wiring is faulty. If it stays on the same port, suspect the board. Swap them back afterwards.
5. Measure the resistance. Power off, unplug the thermistor and set a multimeter to its 200 kΩ range. A 100k NTC reads roughly 100–130 kΩ at normal room temperature; a PT1000 reads about 1,100 Ω. "OL" means open circuit; close to 0 Ω means a short.
6. Inspect the connector and terminals. Look for a pushed-back pin, a cracked latch, melted plastic or a stranded wire that has worked loose from a screw terminal.
7. Replace with the correct part. Fit a thermistor of the same type, seat it fully in the block, tighten its set screw or clamp gently, then re-run PID or MPC tuning (see the calibration guide).

What causes a MINTEMP error

What causes a MAXTEMP error

Thermistor types and firmware settings

If you replace a thermistor or hotend, the firmware must be told which sensor it is. The wrong type gives readings that are off by tens of degrees, which can cause MAXTEMP, poor extrusion or runaway errors. Printers with closed firmware (Bambu Lab, Prusa, Creality OS) handle this for you, so just buy the official replacement part.

Where the limits live in firmware

// Configuration.h
#define TEMP_SENSOR_0       1    // hotend sensor type (1 = EPCOS 100k)
#define TEMP_SENSOR_BED     1
#define HEATER_0_MINTEMP    5
#define HEATER_0_MAXTEMP  275
#define BED_MINTEMP         5
#define BED_MAXTEMP       150
#define HOTEND_OVERSHOOT   15    // highest target you can set = MAXTEMP - 15

[extruder]
# keep your existing pins; change only what matches your hardware
sensor_type: ATC Semitec 104GT-2
min_temp: 0
max_temp: 290      # what your hotend and thermistor are rated for

"Cold extrusion prevented" is not a MINTEMP fault

A separate check blocks the extruder motor when the nozzle is too cold to melt plastic. It protects your extruder gears and isn't a hardware fault. Marlin shows cold extrusion prevented below 170 °C, Klipper shows Extrude below minimum temp (its min_extrude_temp also defaults to 170 °C), and Creality OS shows TE2111. Heat the nozzle to printing temperature and try again. If it appears mid-print, the nozzle temperature dropped, which is a thermal runaway-type problem worth investigating.

How to prevent thermistor errors

• Strain-relieve the toolhead cable so the wires don't flex at the same point on every move.
• Keep a silicone sock on the heater block, and replace it when it tears.
• Check toolhead connectors and screw terminals as part of your maintenance schedule.
• Use ferrules on stranded wires in screw terminals.
• Keep a spare thermistor of the exact type on the shelf.
• After any hotend or thermistor swap, confirm the sensor type and re-run PID or MPC tuning.

Frequently asked questions

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