Temperature sensor NTC 100k

The G1 extruder has three NTC 100k thermistors — one per heating zone — that measure barrel temperature. The reading is handled directly by the main Octopus board, which feeds it to Klipper.

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Specifications

Parameter	Value
Type	NTC (Negative Temperature Coefficient) thermistor
Resistance at 25°C	100 kΩ
Operating range	0–300°C (Klipper firmware minimum is 0°C)
Read by	Octopus board (not the extruder_board)
Klipper type	NTC 100k resistance/temperature table

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Location

One sensor per zone, embedded in the barrel wall next to its heater cartridge:

Zone	Position
Feeding Zone (Zone 1)	Upper barrel section, near hopper
Melting Zone (Zone 2)	Middle barrel section
Nozzle Zone (Zone 3)	Lower barrel section, near nozzle

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How it works

The thermistor’s resistance changes with temperature. The Octopus board reads this resistance and Klipper converts it to a temperature using a resistance/temperature table. Klipper then drives the heater (via the extruder_board relays) to hold the target.

The signal path runs: sensor at the extruder → JST at the extruder → ethernet cable (panel box → extruder breakout) → JST on the Octopus.

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The main fault: an open connection (not the sensor)

If any connector along the path opens, the reading jumps to absurd values such as ~-90°C, and Klipper raises one of:

• extruder below minimum temp
• temperature not valid (the firmware minimum is 0°C, so a negative reading is rejected)
• not heating as expected

On the temperature graph this shows as sudden, drastic jumps.

Caution

It is almost never the sensor itself — check the connections first. The three points that commonly open the circuit are:

1. The JST on the Octopus for the temperature sensor
2. The ethernet cable running from the panel box to the extruder breakout
3. The JST at the sensor, at the extruder

Don’t confuse it with a heater problem

A zone that does not heat or heats too little is usually a heater/relay issue, not the sensor:

• Heats too little / erratically → the relay may not be switching (see extruder_board)
• Does not heat at all → a broken heater cartridge (see Heater cartridge)

A sensor fault instead shows as a reading problem (impossible values / jumps), not a heating-power problem.

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Replacement

Danger

Do not redo PID tuning when you touch the temperature sensor — ever. PID tuning has nothing to do with the thermistor. Replacing a sensor only requires its resistance/temperature calibration in the Klipper config (the 3-value R/T curve), not a PID retune.

If a sensor truly needs replacing:

1. Power off the machine and let the barrel cool completely
2. Check the connections first (the JST at the extruder, the ethernet cable, the JST on the Octopus) — confirm the sensor is actually the fault before removing anything
3. Do not force the sensor out of the barrel wall — you can strip the internal M3 thread. If you must remove it, do so gently, with no levering or prying
4. Fit the replacement sensor into the same bore
5. Reconnect the connector
6. In the Klipper config, set the new sensor’s resistance/temperature curve using its 3 calibration values — do not run PID tuning

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Notes

• All three sensors should read similar temperatures when the machine is cold — a large discrepancy (> 5°C) at room temperature suggests a wiring or sensor problem (check wiring first)
• The sensors ship with G1 replacement kits — contact Ginger Additive support for the correct part

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Related notes

• Temperature sensor disconnected
• Klipper MCU extruder_board — heater relays (read of temperature is on the Octopus)
• Heater cartridge
• Multi-Heating Zones
• Heater not reaching temperature