Neptune 4 and 4 Pro: plastic blob on the hotend (blob of death) or leaks around the nozzle

Symptom

During printing the filament sticks to the nozzle and the hotend surface until it forms a blob, or plastic builds up around the nozzle before starting or when stopping.

Likely causes, from most to least likely

1. The first layer detaches from the plate and the nozzle keeps extruding in mid-air.
2. The model has no supports where it needs them or rests on very little area on the bed.
3. The nozzle or heat break is loose and plastic escapes through the thread.
4. A clogged or worn nozzle, a wrong temperature or too high a speed, which makes the filament ooze.
5. A damaged thermistor: the hotend temperature reads below zero.

Checks to tell which one it is

• Power on and check the hotend temperature: if it reads room temperature, the thermistor is fine; if it stays below zero, it may be damaged.
• Heat to the filament's temperature and load 50 mm: if the gear turns but little or nothing comes out, the nozzle may be clogged.
• Check the slicer preview: missing supports or too little contact area.

Before you start

Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.

Step-by-step fix

1. Remove the extruder

   With the printer off, unplug the rear fan and remove its three screws (2.5 mm key) and the six extruder screws (2.0 mm). Rest the extruder on the bed.

   Check: You can reach the blob or the leak.

   If that does not fix it: Go to the next step.

2. Remove the blob while hot

   Power on, set the hotend to 200 °C and, once reached, switch off at the power switch and remove the blob with pliers. To clean leaks, Elegoo uses 220 °C, cutting pliers and a paper towel held with pliers. Wear insulated gloves: the hotend is hot.

   Check: The nozzle and block are free of residue.

   If that does not fix it: If the plastic is very hard, raise the temperature slightly or use a hot air gun.

3. Tighten the nozzle while hot

   So it does not leak again, with the nozzle hot hold the heater block with pliers and tighten the nozzle with a 6 mm socket or open-end wrench.

   Check: The nozzle is firm and does not ooze through the thread.

   If that does not fix it: If the temperature read below zero, replace the thermistor (next step).

4. If the thermistor reads below zero

   Remove the hotend, soften the blob with a hair dryer without blowing hot air on the extruder housing (it deforms), remove the blob and replace the thermistor. Elegoo specifies a high-temperature NTC 100K (300 °C) with a 2-pin PH2.0 connector.

   Check: The screen shows room temperature.

   If that does not fix it: Contact Elegoo support.

5. Reassemble and re-level

   Refit the toolhead. With the nozzle cold, put the black silicone sock back on. Then re-level and set the Z offset.

   Check: The first layer prints well and the leaks do not return.

   If that does not fix it: Contact Elegoo support.

Prevention

• Do not leave the printer alone until the first five layers are done.
• Check the slicer preview: enough supports and contact area.
• Keep the silicone sock on and the nozzle properly tightened.

Still not fixed?

Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.

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Printers it applies to

Elegoo Neptune 4 and Neptune 4 Pro.

Official sources

This guide summarises the official documentation linked here:

• Neptune 4 & Neptune 4 Pro - Blob of Death and Filament Leakage · Elegoo
• Nozzle Oozing Cleaning (Neptune 4 Pro) · Elegoo