Clogged hotend (MK4) | Prusa Knowledge Base

A clogged nozzle or hotend is a common issue for FFF/FDM printers. If there are no issues, the filament is pushed in the hotend, melted, and then extruded through the nozzle. However, if the nozzle is damaged or there are impurities in the filament it might get stuck in the hotend, clogging the printer.

How to spot clogged nozzle/hotend?

Visual check

Is the filament reaching the nozzle? Check if the filament goes past the Nextruder gear.
Is the filament coming out of the nozzle? Pay attention when loading the filament.
Partial clog - gaps and missing layers
Partial clog - filament curling up and sticking to the nozzle

Soundcheck

Check if there are clicking noises from the extruder

If there is a loud clicking noise, this most likely suggests the nozzle is clogged or deformed
If there is a light clicking noise, this can most likely point to the gearing

Partial clog

Sometimes the clog is partial, meaning that the printer is able to push some filament through, but it is not enough to print the object properly, leading to visible gaps and missing layers. An early sign of a clogged nozzle is that the filament is not extruded consistently, curls up, and sticks to the nozzle.

Extruder clicking

The hotend or the nozzle is partially or fully clogged and the internal resistance against the flow of the filament is greater than what the gears are able to push. As a result, the gears are skipping leading to the “clicking” noise and in most scenarios also to the grinding of the filament.

How to fix the clogged printer?

Choosing the right method depends on whether you are able to at least partially load/unload the filament or whether the printer is fully jammed and refusing the move the filament even a little.

Before you start fixing the printer, try unloading the filament and removing it completely. If you are unable to do it, it might indicate a more serious problem, but we will deal with this one as well.

Also, move the extruder upwards from LCD Menu - Settings - Move Axis - Z-axis or by long-pressing the control knob, this way you will get better access to the parts that are clogged.

Extruder idler screws

The extruder includes two idler tension screws, to set the correct distance between the drive gear and the two driven gears. These are set to the optimal position at the factory. In case of an intervention on that part, you can adjust the idler tension screws to their optimal position: the tips of the screws must be aligned with the front surface of the Idler Nut. After that, close the Idler Block.

Gears

Over time, a deposit of filament debris can form in the grooves of the feeding gear, which then causes insufficient filament extrusion. Access the extruder by lifting the Idler Nut, and then moving the Idle Shaft. You can blow away the dirt with compressed air, or use a brass brush or an ordinary toothpick. Use the access hole on the side of the extruder.

Nozzle

Do not touch the hotend while the printer is at a hot temperature. Heated parts can cause severe burns!

Follow these steps to clean the nozzle:

Heat the nozzle to the appropriate temperature according to the filament material you will be printing from. First, introduce the filament, then insert an acupuncture needle (included in the package) or a thin wire (0.3-0.35 mm) into the nozzle from below to a depth of approximately 1-2 cm. Use protective gloves if material suddenly starts to flow from the nozzle.
Select the Load Filament option from the LCD menu and check that the nozzle is actually pushing the filament.
Insert the wire or acupuncture needle into the nozzle again and repeat the whole procedure several times. If the filament is extruded correctly, the nozzle is clean.

Are you still having issues? Contact our support team and let them know that you tried to fix the issue with these instructions. We will take it from there.

14 comments

Sandrine P

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5 months ago

I had the same issue, twice in six months.
I tried all the knowledge db suggestions and all of the above. I removed the hot end, replugged it on the printer with max temp, and pushed stuff from the top and bottom. The needle goes through but the filament does not. I removed it completely, used a torch lamp and pushed some pressured air with a compressor until no more filament went out and air was coming out from the bottom. But once on the printer, the filament never reaches the little brass part.It seems like something solid that's not melting above 290° is stuck there. A piece of metal maybe?This is driving me nuts because now I have to order a new nozzle (at least one) and I agree, 22€ might not be much, but with the 8€ for delivery, that's 30 bucks and how-don't-know-how-long I'll wait for the package to come.And 22 bucks every 6 months is even more than I spent on prusament (I don't even print so much !!!)I wish we could have a better answer from support than "sometimes, to replace the nozzle is the only solution". I never had to change the nozzle for every 2kg of printed PLA on my MK3S, I don't see why I should on a brand-new printer!If I was sure it would not happen with a high-flow ObXidian nozzle, I would give it a try, but if I have to change it in 6 months, I will throw the printer through the windows to see if it flies better than it prints...Come on, @support, tell us what investigation and solution you have for that issue, pleeeeeeeeeaaaaassseeeeee....

MagnusVesper

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6 months ago

Are the wires safe to use with the high flow nozzles? (both the Prusa and E3D ones)

Jan Kratochvíl

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6 months ago

Hello. Yes, it is safe to use it, but watch out, as there are 3 to 4 canals inside the nozzle.

Wayne

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7 months ago

My MK3.9 began under extruding everything after many months of good use. To make a long story short (involving all the diagnostics on this page and more), I finally figured out that the extruder idler had deformed such that there wasn't enough pressure against the gear, regardless of tightening the screws. I printed a new pair, i.e. the two halves (idler-lever-a and idler-lever-b), using PC Blend this time, and am back to happy printing. (Having at least 2 printers is important for this kind of failure).

MiSeeger

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8 months ago

The same thing happened to me: The filament broke off right at the top of the tube and the nozzle of my MK4 was clogged. So after removing the nozzle, I tried to get the stuck filament out somehow. In the end, I heated the upper end with a heat gun so that the heated filament poured out. Using a 2mm drill bit, I was able to remove some of the hot filament from the tube by hand using drilling movements. That was a start. After the nozzle had cooled down again, I carefully drilled the solidified filament out of the tube as far as I could with the drill using a cordless screwdriver. This gave me enough space to insert a sturdy wire with a diameter of 1.9 mm into the tube as a test. This worked great. So I used the hot air gun again to heat the front part of the nozzle. I held the nozzle above the heatbreak with pliers without pressing too hard. When the nozzle was hot enough (some filament was already coming out of the front), I was able to carefully push the filament out of the nozzle using this wire. I repeated this procedure a few times until no more filament came out of the nozzle. After the nozzle had cooled down completely, I reinstalled it, inserted some filament and ... voila ... the nozzle was ready for use again.

Wimmer

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12 months ago

printing with 0,25 nozzle get glogging removed the nozzle, dril a whole in a peace of aluminium, tap,threath screw the nozzle in the threath hole use a heatgun and and you can remove it with help of some filament to get it out, you own easy hot ore cold pull debrie in gear ? use you vacuum cleaner It takes me less than 3 minutens to change the nozzle with help of the downloaded tool from printables. the heat block stay in place debris is then also easily removeble I advice every body to use the tool from printables, now I change the nozzle more frequently for 0,6 withs print very good even threath is going well If you object must be strong use 0,8 ore detailed 0,25check always if you filament is brittle, if so dry it 'Also to avoid trouble . when you remove the filament wait until it is really out of the nozzle / gear he does the unloading in two steps, I was not patient, so it broke off

sudo_grue

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9 months ago

Out of curiosity, are you printing with an enclosure? I share a similar problem and am discovering I made the mistake of printing PLA with enclosure closed.