Temperature sensor disconnected

One of the three NTC 100k thermistors on the multi-zone extruder pulled out of its brass insert or has its connector unplugged. The firmware reads an invalid temperature on that zone and refuses to operate.

Note

Sensor specs: NTC 100k Ω, beta 3950, M3 thread. Replacement sensors must match these parameters exactly or temperature readings will be inaccurate.

Symptoms

• Display shows an abnormal or unread temperature on one of the heating zones (Feeding / Melting / Nozzle)
• The machine refuses to boot or stops mid-print with a heater error
• Visually: a sensor wire dangles loose near the extruder
• The brass insert holding the sensor has come unscrewed from the barrel

Possible causes

1. Sensor pulled out during shipping or assembly — the brass insert backed out and the sensor came with it
2. Connector unplugged — the black connector at the back of the extruder wasn’t fully seated
3. Soldered joint failed — rare, but can happen on the wire-to-sensor solder

Diagnosis

Ask for a clear photo of the front of the extruder showing all three sensors. Identify:

• Which zone is affected (top = Feeding / Zone 1, middle = Melting / Zone 2, bottom = Nozzle / Zone 3)
• Is the sensor itself pulled out, or just the connector unplugged?
• Is the wire intact or damaged?

Fix

Case A — Sensor pulled out, sensor itself intact

The sensor is an NTC 100k in a brass insert that screws into the barrel.

1. Identify the sensor — small black/metallic cylinder in a brass insert
2. Reinsert the brass insert into its threaded hole on the barrel — do not rotate the sensor wire
3. Tighten the brass insert only, never grip the wire
4. If the customer has a crimping tool:
   • Re-seat the sensor in its connector
   • Crimp and reconnect
5. If the customer does not have a crimping tool (common):
   • Bypass the black connector: cut the connector off
   • Splice the sensor wires directly to the spare-sensor wires
   • Insulate the joints carefully (heat-shrink or electrical tape)

Case B — Connector unplugged (sensor and wire intact)

1. Locate the black connector at the rear of the extruder
2. Reseat it with the safety clip facing up
3. Listen for the click confirming it’s locked

Case C — Sensor failed or wire damaged

• Use the spare sensor included in the G1 kit (a duplicate is provided as backup)
• If no spare available, request a replacement from Ginger Additive support

Verification after the fix

1. Run Firmware Restart
2. Check the temperature reading on the affected zone:
   • It should be close to room temperature (similar to the other two zones, ±5°C)
   • If it still reads “disconnected” → connection isn’t solid, redo it
3. Heat the extruder to 200°C and watch the reading climb steadily
4. Compare the heating curve with the other two zones

PID calibration after sensor replacement

You do NOT need to re-run PID calibration after replacing a temperature sensor — and you should not.

PID has nothing to do with the thermistor: PID values are calibrated to the heater cartridge and barrel thermal mass, not to the individual sensor. A replacement sensor only needs its resistance/temperature curve (the 3 calibration values) set in the Klipper config — not a PID retune. See Temperature sensor NTC 100k.

How to prevent

• Don’t pull on the extruder wires when moving the machine
• At first assembly, verify all brass inserts are tight before powering on
• Train operators to support the extruder body, not the wires, when handling

Case D — Fan-induced temperature drop (thermal runaway shutdown)

Symptom: temperature on Zone 3 (Nozzle) drops suddenly by 20–30°C during printing → firmware throws a thermal runaway error and stops the print.

Cause: the left cooling fan (part-cooling fan on the extruder) is tilted too far downward and blows directly onto the Zone 3 temperature sensor, causing it to read falsely low. The heater tries to compensate, but if the drop is faster than the PID can respond, it triggers a safety shutdown.

Diagnosis:

1. Watch the Zone 3 temperature live in Mainsail while the fan is running
2. If the temperature dips when the fan turns on → fan position is the cause

Fixes:

1. Rotate the fan so it is more horizontal and points away from the sensor
2. Recalibrate the PID for Zone 3 with the fan running at operating speed — this teaches Klipper how to compensate for the airflow. PID calibration is automatic and takes ~5 minutes (run PID_CALIBRATE HEATER=extruder in Mainsail console)
3. Newer G1 versions have a redesigned fan duct that redirects airflow away from the sensor

Note

Observed in 5+ customer cases (recurring pattern). After fan repositioning or PID re-tune, the issue is resolved.

Case E — Faulty connector crimp causing temperature reading spikes

Symptom: Temperature readings show impossible jumps — e.g. drastic drops to ~-90°C, or sudden ±20°C swings that cannot reflect real thermal behavior. Klipper typically raises extruder below minimum temp, temperature not valid (firmware minimum is 0°C), or not heating as expected, and may refuse to heat the zone.

Why it happens: The NTC 100k thermistor works by resistance measurement. A partially open circuit (bad crimp inside the connector housing, or isolation cover blocking the metal contact) produces a resistance value the firmware cannot map to a real temperature — it reads as an impossible spike. Unlike a fully disconnected sensor (which reads “disconnected” immediately), a faulty crimp can cause intermittent contact and random-looking jumps.

Where to check (in order):

1. Panel Box → Octopus board — inspect all thermistor connector terminals for loose or improperly crimped contacts; the metal contact can sit inside the plastic housing but not actually pierce the insulation
2. Ethernet-style cable — the sensor wires route through an RJ-style cable; check that all crimp pins are fully seated
3. Extruder-side connectors — any connector between the sensor and the board

Diagnostic tip: Gently wiggle each connector while watching the temperature reading live in Mainsail. If the reading jumps when you move a specific connector, that is the faulty contact.

Fix: Re-seat or re-crimp the faulty connector. Note: the connector housing often cannot be inspected without breaking it open — if in doubt, replace the connector. In-field fix: cut the connector off and splice the wires directly (see Case A procedure). Contact Ginger Additive support for replacement connector kits.

Notes

• Pattern observed mostly at first assembly: the middle (Melting) sensor is the one most often shipped loose
• Connector bypass is a common in-field repair when a crimping tool isn’t available — it works perfectly when properly insulated
• Fan-induced drop (Case D) is the most common cause of unexpected mid-print temperature errors when sensors are otherwise correctly installed
• Faulty crimp (Case E) is distinguished from Case D by the pattern: random large jumps (including negative values) vs. steady drop linked to fan activity

Related notes

• Temperature sensor NTC 100k
• Extruder
• Multi-Heating Zones
• Heater cable disconnected
• Firmware restart