When Klipper on the Elegoo Neptune 4, Neptune 4 Pro, Neptune 4 Plus, or Neptune 4 Max aborts with “Heater extruder not heating at expected rate,” the printer has detected that nozzle temperature is rising too slowly during warm-up. Klipper monitors the rate of temperature climb and triggers this safety shutdown when the measured rise does not match its expectation — protecting the hardware from a runaway or failed heater condition.

What the Error Means

The Neptune 4 series uses a ceramic or resistive heater cartridge seated inside the hotend heater block. Klipper expects the nozzle temperature to rise at a defined minimum rate after the heater is commanded on. If it climbs too slowly, Klipper concludes the heater is not generating adequate heat and shuts down. The three main causes are: a voltage mismatch (if the printer is connected to the wrong mains voltage), a loose or intermittent heater cartridge connector at the hotend adapter board, or a failed heater cartridge. A damaged adapter board pin that is not making solid contact with the cartridge cable is a secondary cause.

Step-by-Step Fix

1. Check the printer’s voltage selector switch, if present, on the power supply. Confirm it is set to match your local mains supply (110 V for North America, 220–240 V for Europe and most of the rest of the world). A mismatch will severely under-power the heater.
2. Power off the printer and locate the ceramic heating element connector at the hotend adapter board (the small PCB at the hotend). Unplug it, inspect the pins for corrosion or discoloration, and reseat it firmly.
3. Check the adapter board pins — if a pin is bent or the connector housing is cracked, the heater may not be receiving full power.
4. Measure heater cartridge resistance with a multimeter. Disconnect the heater from the adapter board and probe the heater cartridge terminals directly. A 24 V heater cartridge typically reads approximately 10–20 Ω depending on wattage; check the Elegoo Neptune 4 wiki for the exact spec. An open-circuit (OL) reading confirms a failed cartridge.
5. Replace the heater cartridge if it is open-circuit. Use an Elegoo-specified replacement to match the voltage and wattage.
6. If the cartridge tests good, the adapter board itself may be faulty. Contact Elegoo support for a replacement hotend adapter board or heater assembly.
7. Run FIRMWARE_RESTART in the Klipper console (via the web UI) after fixing the underlying issue to clear the fault before attempting to heat again.

Parts Required

• Replacement heater cartridge (Neptune 4 series spec — 24 V, correct wattage)
• Multimeter (for resistance and continuity testing)
• Replacement hotend adapter board (only if board is confirmed faulty — via Elegoo support)

Contact Elegoo support if the error persists after cartridge replacement — a power supply fault delivering incorrect voltage is also possible and requires professional assessment.

Frequently asked questions

What does Elegoo n4-heater-not-heating mean?

When Klipper on the Elegoo Neptune 4, Neptune 4 Pro, Neptune 4 Plus, or Neptune 4 Max aborts with "Heater extruder not heating at expected rate," the printer has detected that nozzle temperature is rising too slowly during warm-up. Klipper monitors the rate of temperature climb and triggers this safety shutdown when the measured rise does not match its expectation — protecting the hardware from a runaway or failed heater condition.

How do I fix Elegoo n4-heater-not-heating?

Klipper aborts with 'Heater extruder not heating at expected rate' on Neptune 4. Learn to check voltage, reseat the heater connector, and test cartridge resistance.