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3D Printer Nozzle Clogs: Symptoms, Causes and Fix

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Featured image - the clogged nozzle on a 3D printer.
Anker Maker 3D Pinter.

In the world of 3D printing, nozzle clogs can be a pain. They can also cause major problems, adversely affect the operation of your printer and cause the failure of your prints.

We are of course talking about FDM (Fused Deposition Modelling) 3D printing rather than resin, and the nozzle is where the extruded filament emerges once heated. 

The nozzle then is the business end of the 3D printer, and any clogging will render the machine pointless. There can be many reasons why the nozzle will clog or become blocked, and we’ll be looking at these in more detail throughout.

As we’ve said, the ultimate downside of nozzle clogging is the failure of your print.

It can reduce the quality of your prints with visible layer lines or even damage the extruder motor, the print bed, and the hot end.

In extreme circumstances, there is also the potential of overheating and subsequent fire risk. 

Probable causes of nozzle clogging can be varied, but most commonly will be down to improper bed levelling, incorrect temperatures and air locks among others. With variable causes come varied solutions.

In this article, we’ll be looking at both the cause and solution and try to help you avoid nozzle clogging altogether if possible.

Common Symptoms of 3D Printer Nozzle Clogs

The best way to find the cause of a problem is to work back from the symptoms it has caused.

These symptoms can either be plainly visible or may need some more detailed investigation to identify correctly. So, let’s take a look at some possible symptoms of a nozzle clog.

The definition of a nozzle clog is where something is preventing the filament from extruding through said nozzle. This could be caused directly at the nozzle itself or maybe further back to the hot end, Bowden tube, or extruder motor.

But what are the symptoms we should be looking for?

No filament being extruded

The filament is not coming through the nozzle at all, although the extruder motor is still working and trying to push new filament through.

This could be characterized by the obvious fact that the model isn’t printing. Another indication would be that the extruder motor is “skipping” and this would likely cause a knocking sound. 

Reduced filament extrusion

The filament is coming through, but not evenly. This can be visible on the print bed, particularly on the initial layers or support raft.

You may also notice that your unused filament spool isn’t reducing or rotating as expected.

Replacement filament won’t feed through

If you’re changing the roll of filament and try to manually feed it through the nozzle, you may find that it simply won’t go through the nozzle

Build up of extruded filament on the hot end

The filament may be coming through the nozzle, but building up into a clump on and around the heating block. This may be due to more external factors, but could also be a symptom of a partial nozzle clog.

Common Culprits of Nozzle Clogging in 3D Printers

We’ve looked at some possible symptoms of nozzle clogging, so let’s now look at some possible causes.

These are probably the main ones that you may experience, but others could crop up depending on your particular printer setup.

In most cases, the problem would be apparent due to the lack of filament coming through your hot end nozzle.

Dirty or damaged nozzle

The most commonly used material for nozzles is brass and, over time, this can easily become worn or damaged.

Constant heating and cooling can have a detrimental effect on the nozzle, and this would be evident in the quality of the print.

A dirty nozzle may leave marks on the filament itself which would be visible, particularly on lighter colors. 

Damage to the nozzle would also be apparent, as it can lead to “blobs” of filament depositing randomly. The nozzle could also become pinched, leading to under extrusion and gaps in your printed model.

Both of these would be due to a change in the shape and size of the nozzle point itself. The causes of this can be many, but most likely to be wear and tear.

However, if you’re using a particularly abrasive filament (wood, carbon fiber, etc.) then this will cause damage more quickly.

Incorrect print settings

In order to achieve a decent printed item, you need to have the correct settings for your printer.

This can be tricky for first time users and is something that may take trial and error to get right. The error part comes into play though when your settings cause a nozzle clog.

Settings that could be a contributory factor to a clog could be the print speed, extrusion rate (e-steps), extraction rate and nozzle temperature.

Another more common setting that can be overlooked in terms of nozzle clogging could also be the print bed levelling or the nozzle being too close to the bed.

Let’s have a little closer look at each of these issues:

Print speed

This would be in comparison to the nozzle temperature set for the filament type you’re using.

If your speed is too high for a filament that prints at a lower temperature, then it will be pushed through the nozzle before it has time to heat.

The opposite is true if the speed is too low for higher temperature filaments, as it can then build up on the nozzle, causing it to clog.

Extrusion rate

This is also called the “e-step” and is the rate at which filament is pushed though the nozzle by the extrusion gear.

Having this setting wrong can lead to both under- and over-extrusion.

Filament over-extrusion example.
Visible filament over-extrusion on test cubes, source: Donnysaysvacuum via Reddit

Under-extrusion will make your print fragile and leave gaps, but it’s over-extrusion that’s more likely to cause a clog.

E-steps can be tricky to set up, but it’s worth looking into. However, we won’t have time to do that in this article.

The basic premise is that, if you want to extrude 100 mm of filament, then your e-steps should be calibrated to ensure that is what’s extruded. If the e-step is wrong and causes over-extrusion, this can lead to a clogged nozzle.

Extraction rate

Similar to the extrusion rate, but more based on speed rather than filament length.

Extraction stops the filament from extruding to allow movement across the print to another area.

If we don’t set the correct extraction, then we can face a “stringing” issue. This can also lead to a build-up of filament and subsequent clog.

Stringing test image.
Stringing test results, source: thingiverse.com by Andy Pants

Bed levelling

A level print bed is essential to the success of any print, so you should check it regularly.

If the bed is not level, then there will be areas where the nozzle is too close to the surface.

In such cases, the filament will still extrude but will have nowhere to go but back from where it came!

Even with a level print bed, the Z-axis offset may be set too low. This would again cause the nozzle to be too close to the print bed.

The same nozzle clog would then be the result.

Incorrect filament type or diameter

It’s important to use the right nozzle for the right filament.

We’ve already looked at how abrasive filaments can cause nozzle damage, leading to clogs. So what other factors are we looking at here?

The most commonly used diameter of filament in FDM 3D printing is 1.75 mm, with the most common nozzle diameter being 0.4 mm.

There are, however, nozzles available with a diameter of anything from 0.1 mm to 1.0 mm.

Some filaments are also available in 2.75 mm diameter, but this isn’t used so much by the average printer.

In fact, there are very few “home” 3D printers which can cater for 2.75 mm filament. However, here lies the problem and also the answer.

If you use the wrong combination of filament diameter with nozzle diameter, then you’re heading straight for an inevitable nozzle clog. 

Poorly assembled extruder/ Bowden/hot end set-up

A quite common cause of a nozzle clog is air getting into the extrusion system.

The key part of this particular set-up is the Bowden tube, and it’s therefore important to ensure that both ends are secure, tight, and cut straight.

Damage can occur to the ends of the tube and also to the compression couplings, so regular maintenance is advised here. 

Any other gaps between the tube, heat-break, or nozzle can also allow air intrusion and can then lead to a nozzle clog.

This can be the trickiest part of your printer to clean or repair, but let’s now look at how you’d go about that and the other clogs we’ve discussed.

How To Unclog and Clean a 3D Printer

Obviously, you’d be hoping to avoid a nozzle clog in the first place, but they unfortunately still happen.

We’ve looked at how they occur, so let’s now look at how to remedy the problem.

In most cases it will be apparent that the actual clog is at the nozzle, so you’d need to clear that before working back to the root cause.

This is a fairly straightforward process but does carry some safety risks, so be careful when you’re doing this. In all cases, you’ll need to have the nozzle at the working temperature to your blocked filament before you start. 

The first step will depend on how bad the nozzle clog is and if the nozzle appears damaged.

If there is no damage and no external filament covering the nozzle, then you may just be able to unblock it. For this you will need a nozzle cleaning needle which may have come with your printer.

Nozzle cleaning needle.
Cleaning needle, source: 3DprintingGeek

If not, they are fairly cheap to buy from various online outlets. Make sure the nozzle is hot as previously advised, and then you can start.

The needle will be very slightly smaller in diameter than your nozzle, and you will need to insert it into the nozzle hole.

This can be a bit difficult as the sizes are so small, but with practice it becomes easier.

This will clear the clog and when you withdraw the needle it will have filament on it. You may need to do this a few times to remove the clog completely.

Hopefully, that simple method will be enough to clear the nozzle clog but, in some cases, things can be a lot worse.

Let’s look at how to clear a particularly bad nozzle clog and put your printer back to working order:

  1. Heat the nozzle: This should be to the working temperature of the filament you’ve been using. 
  2. Remove the filament: If filament is still fed through the tube to the hot end, then pull this back to completely remove it.
  3. Remove any debris filament: You may see that filament has heated and formed around the outside of the nozzle and indeed the heating block. Carefully remove this with a suitable tool. A soft, wire brush can be good, or even a small metal palette knife. Remember though that there are electrical wires connected to the block, so avoid touching or damaging them. 
  4. Undo the nozzle: Again with caution as it’ll be hot, unscrew the nozzle and set it to one side to cool. Once cooled, you will probably just need to dispose of it safely.
  5. Clear any further clog: You may find that there is a larger blockage backup through the heat break and even into the Bowden tube. Undo the compression coupling and remove the tube from the hot end assembly. Hopefully, you’ll find any filament that is still present in the hot end and can then remove this using the nozzle cleaning needle. You may be better served using a larger, wire brush to clean the inside of the heat break, etc. Again, these are widely available through online outlets. 
  6. Clear/cut the Bowden tube: If you’ve removed the tube from the hot end assembly, then there is likely to be filament present around and inside the end. The best way to remedy this is to cut the end to remove the dirty/damaged section. It’s important to get the cut dead straight to avoid the air problems that we mentioned earlier.

Clearing any filament or dirt from the printer should be possible using the tools that we’ve discussed. You may also want to use a cleaning solution or solvent to ensure a perfect job.

Please remember though that you will need to turn the printer off before using any chemicals that may be flammable or toxic. 

Once you’ve successfully cleared the nozzle clog, and cleaned and repaired your printer, you’ll need to reassemble it.

You’ll need to have the printer on and the nozzle up to temperature again to do this, but it should be a simple case of reversing the disassembly steps.

Final Thoughts

I hope I could give you some insight into why your 3D printer’s nozzle may have clogged. But mainly how to go about fixing and cleaning your printer afterward.

The best thing would be to avoid nozzle clogs altogether. Regular maintenance and checks on the printer settings can definitely help with this. 

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Affiliate Disclosure:

All our reviews are based on our personal experience and deep research. We are supported by our partners, and we might earn commission from qualified purchases through affiliate links with no additional costs for the buyer. Read more.

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