Description

Prusa Nextruder Heatsink Thermistor NTC 100K — Cold Zone Temperature Monitoring

This is the OEM replacement NTC 100K thermistor for the Prusa Nextruder heatsink — the sensor that monitors the temperature of the cold zone above the melt area. Unlike the hotend thermistor which reads nozzle temperature, this heatsink thermistor detects when the cold zone is getting too warm — an early warning of heat creep before it causes a filament jam.

If your printer is reporting heatsink temperature warnings, showing erratic cold zone readings, or the heatsink thermistor has physically failed, this is the direct replacement.

What the Heatsink Thermistor Does

The Nextruder uses two thermistors — one in the heater block (measuring nozzle temperature) and one in the heatsink (measuring cold zone temperature). The heatsink thermistor provides real-time feedback on whether heat is creeping upward from the melt zone into the cold zone. If the cold zone temperature rises above a safe threshold, the printer can warn you or pause the print before a jam occurs.

Without a functioning heatsink thermistor, the printer loses its ability to detect heat creep in advance — meaning the first sign of a problem is a jam, rather than a warning you can act on.

When to Replace

Heatsink temperature warnings or errors on the printer screen, erratic or jumping cold zone temperature readings in the printer dashboard, thermistor physically damaged — cracked, cut, or exposed wiring, readings that don’t change when the hotend heats up (stuck sensor), and as part of a Nextruder hotend rebuild or heatsink replacement.

What’s Included

Heatsink thermistor NTC 100K × 1 (90 mm wire length)
M3x4 grub screw × 1 (for mounting)

Not included: heatsink, heater block, hotend thermistor, nozzle, or other hotend components.

Compatibility

Prusa MK3.9 / MK3.9S
Prusa MK4 / MK4S
Prusa CORE One / CORE One+
Prusa CORE One L

Not compatible with: Prusa XL (uses a different heatsink thermistor), MK3/MK3S/MK3S+ (no heatsink thermistor on V6 hotend), or Prusa MINI/MINI+.

Installation

Refer to the Prusa Knowledge Base repair manual for your specific printer model at help.prusa3d.com. The thermistor mounts into the heatsink and is secured with the included M3x4 grub screw. Ensure the thermistor bead is seated correctly in the heatsink bore for accurate readings.