6 sourced reports, with what to check before you buy. Each one links to the page it was reported on.
Costly or dangerous
Blob of death forces full extruder replacement
From a Polish professional review (ithardware.pl). Before a firmware update, the printer lost Z-offset settings on power-off, causing poor first layers. When the reviewer forgot to re-level, a 'blob of death' formed around the nozzle, completely clogging the hotend and requiring a full extruder replacement (Elegoo sent a new one under warranty).
What to check. The Z-offset loss issue was firmware-related and reportedly fixed by updating. But if you see poor first-layer adhesion, fix it before it becomes a blob of death — a full extruder replacement is the cost of ignoring it.
From Elegoo's official wiki. The Neptune 4 series uses a customized Klipper build; updating firmware via Fluidd (rather than Elegoo's official method) is incompatible and can brick the printer. Recovery requires an eMMC adapter and fix pack flashing.
What to check. Never update Neptune 4 Plus firmware through Fluidd. Use only Elegoo's official firmware update process (fix pack + motherboard + touchscreen firmware). A bricked unit requires hardware recovery via eMMC adapter.
Neptune 4 Plus/Max MCU shutdown from damaged thermal sensor
From Elegoo's official troubleshooting wiki for the Neptune 4 Plus/Max. The printer halts with an MCU shutdown error when the thermal sensor reads out of range. Elegoo identifies a damaged thermal sensor as the most likely cause, with wiring damage as a secondary possibility. This is a safety shutdown that stops prints and requires diagnosis.
What to check. If you see 'MCU mcu shutdown: ADC out of range', first reseat the sensor cable and check for bent pins before replacing the thermistor. The printer will halt prints until resolved.
Nozzle temperature runaway to 300°C+ after hotend replacement
French owner forum thread. After replacing the extruder kit, the nozzle temperature climbed uncontrolled past 300°C until firmware faulted and smoke escaped from the ceramic plate. A forum reply notes the thermistor may be short-circuited. This is a thermal runaway scenario with fire risk.
What to check. If you replace the hotend, verify the thermistor reads correctly before powering on. An uncontrolled temperature climb past 300°C indicates a shorted thermistor or heater fault — power off immediately.
Z-offset not saved causes failed first layers and blob of death
Verified buyer review on 3DJake (German). The printer starts too high despite leveling, parts don't adhere, and during unattended printing the print head gets covered in a large blob of PLA. The user also reports a firmware error preventing nozzle heating for cleanup, forcing full disassembly after only 3 prints.
What to check. Z-offset reliability is a known weak point. Verify first-layer adhesion on every print and don't leave long prints unattended until you've confirmed the offset holds. A blob of death can destroy the hotend assembly.
Layer shifting from loose X/Y timing pulley set screws
From Elegoo's official wiki. Layer shifting on the Neptune 4 Plus can be caused by loose set screws on the X/Y timing pulleys, damaged belt tensioners, or belts that are too tight. This is a mechanical issue that produces visibly shifted layers.
What to check. If you see layer shifting, check the pulley set screws and belt tension before assuming a firmware or slicer issue. A 2.0mm Allen key is all you need to tighten them.
These reports come from the pages linked under each item: owner forums, repair guides and workshops. They are not a diagnosis of any one unit, and a careful check of the one you are buying still applies.
Text from the Kriko 3D printers catalog, version 0.1.1, under the CC-BY-SA-4.0 license.
