3D printer not printing: diagnose and fix the most common faults

"Not printing" covers a surprisingly wide range of faults, from a complete failure to extrude any filament to prints that start fine then fail mid-way. This guide works through the most common causes in the order they are easiest to rule out.

Before you start: record your current slicer settings and take a short video of the failure if you can. This makes it easier to track what you have already tried, and if you end up sending the machine in for repair, it gives a technician a clear starting point.

Step 1: Check the obvious things first

A surprising number of "it just stopped working" faults turn out to be one of these:

1. Is the filament still loaded? Open the extruder arm or idler lever and check whether filament is actually inside the tube and touching the drive gear. 2. Is there filament left on the spool? Check the weight or give it a spin — an empty spool feels noticeably light. 3. Is the build plate level? Most printers need the first layer to be within about 0.1–0.2 mm of the nozzle. Even a small knock can shift the bed enough to cause failures. 4. Has anything changed since the last successful print? A new filament brand, a new slicer version, or moving the printer to a colder room can all cause prints to fail without any obvious hardware fault.

Step 2: Find out whether filament is reaching the nozzle

Do a manual extrusion test:

1. Heat the nozzle to your normal print temperature (for example, 200 °C for PLA). 2. Using the printer's control screen or a host program, command a manual extrusion of 50–100 mm at a slow speed. 3. Watch the drive gear and the nozzle.

Drive gear turns, filament feeds smoothly, plastic comes out of the nozzle: the extrusion system is probably fine. Skip to Step 4.

Drive gear turns but you can hear clicking or grinding, and filament barely moves: the extruder is stripping the filament. Go to Step 3a.

Drive gear turns, filament moves into the hotend, but nothing comes out of the nozzle: you have a partial or full nozzle clog. Go to Step 3b.

Drive gear does not turn at all: the stepper motor or its driver may have failed. Go to Step 5.

Step 3a: Extruder clicking or grinding

Clicking from the extruder (often called extruder skipping) means the motor is stalling because filament cannot move forward fast enough. Common causes:

1. Partial nozzle clog. Even a slight restriction raises back-pressure enough to stall the extruder. Work through Step 3b before adjusting anything else. 2. Print temperature too low. Filament that is not fully melted creates back-pressure. Try raising the nozzle temperature by 5–10 °C in increments. 3. Print speed too high. Reduce print speed to 40–50 mm/s and see whether the clicking stops. 4. Extruder idler tension. On Bowden printers, the idler spring may be too loose (filament slips) or too tight (filament is crushed and cannot feed). Refer to your printer's manual for the correct adjustment. 5. Damaged PTFE tube. On Bowden machines, a gap between the PTFE tube and the nozzle creates a space where molten filament pools and causes resistance. Remove the tube, inspect the end, and trim it square with a sharp knife if it is deformed. 6. Worn extruder drive gear. On older machines the hobbed gear teeth wear smooth. Inspect with a torch — if you can see polished flats where the teeth should grip, the gear needs replacing.

Step 3b: Nozzle clog

A partial clog allows some plastic through but causes under-extrusion. A full clog produces nothing at all.

Try a cold pull first — it is the safest method and requires no tools:

1. Heat the nozzle to printing temperature. 2. Push filament through manually until it flows freely. 3. Drop the temperature to around 90 °C for PLA (check the manufacturer's guidance for other materials). 4. When you reach that temperature, pull the filament out firmly and steadily. It should emerge as a plug carrying debris from inside the nozzle. 5. Repeat two or three times until the plug comes out clean.

If the cold pull fails or you suspect a hard clog from carbonised filament, you may need to remove the nozzle:

1. Heat the hotend to printing temperature — never try to remove a nozzle cold, as you will strip the threads. 2. Counter-hold the heater block with a spanner while unscrewing the nozzle with a socket or nozzle wrench. 3. Soaking a brass nozzle in acetone overnight can dissolve PLA and ABS residue. Acetone will not harm stainless steel or hardened steel nozzles.

Warning: working near a hot hotend carries a real burn risk. Allow the assembly to cool below 50 °C before handling. Take care not to strain the thermistor or heater-cartridge wires while working on the hotend.

Step 4: Slicer and print settings

If manual extrusion looks normal but prints still fail or look poor, the problem is usually in your settings.

First layer not sticking:

1. Re-run your bed levelling procedure. 2. Clean the print surface with isopropyl alcohol (70–99%). 3. Adjust your Z offset — lower the nozzle by 0.05 mm increments until the first layer squishes slightly into the surface. 4. If using a glass or smooth PEI surface, try raising bed temperature by 5 °C.

Print looks under-extruded (gaps, thin walls, weak layer bonding):

1. Confirm your filament diameter setting in the slicer matches the actual filament (usually 1.75 mm or 2.85 mm). 2. Calibrate your extruder e-steps or flow rate. Mark 100 mm on the filament, command a 100 mm extrusion, then measure how much actually moved. 3. Try raising nozzle temperature by 5 °C.

Print starts then fails mid-way:

1. Check the filament spool for tangles — a tangle will gradually tighten until extrusion stalls. 2. Check whether the hotend cooling fan is running. If the heat-break fan stops, heat creep can cause filament to soften too high up the cold zone and jam. 3. Note the layer at which failure consistently happens. Overhangs, bridges, and dense infill regions all create higher back-pressure — a marginal temperature or a partial clog will often reveal itself at exactly these points.

Step 5: Electrical and stepper motor faults

If the extruder motor does not move at all, or moves erratically with no obvious mechanical cause, the fault may be electrical:

• Loose connector. With the printer powered off and unplugged from the mains, check that the extruder stepper cable is firmly seated at both the motor and the mainboard.
• Failed stepper driver. Mainboards have individual stepper-driver chips. A failed driver usually causes one axis or the extruder to stop working entirely while everything else behaves normally.

Important: do not open the mainboard enclosure with the printer powered on. Capacitors on the board can hold charge even after you switch off — always disconnect from the mains and wait a minute before touching internal components.

Replacing a stepper driver typically involves soldering or swapping a driver module, depending on the board type. If you are not comfortable with electronics work, this is a sensible point to consider a mail-in repair.

Step 6: Firmware and communication issues

If you print via USB or OctoPrint and the printer has recently stopped responding:

1. Try slicing and printing directly from an SD card or USB drive to rule out a host-computer or cable fault. 2. Check whether your slicer's start G-code includes a homing or bed-levelling command that may be hanging (for example, G28 taking longer than expected because an endstop switch has failed). 3. Consider rolling back any recent firmware update. Some community firmware builds introduce regressions; factory firmware is a safe baseline while you isolate the problem.

When to mail it in

If you have worked through the steps above and the printer still will not extrude, or if the fault points to a failed stepper driver, a cracked heater block, a shorted heater cartridge, or mainboard damage, the repair usually needs soldering equipment and access to components that are fiddly to source individually. Hark Tech offers a mail-in repair service for 3D printers — describe the fault and what you have already tried via the contact page and we will give an honest assessment of whether the repair is within scope and an estimate of cost before you commit to posting anything. Turnaround is typically within a few working days of the printer arriving.