Hotend Jams are No Fun!

I‘m going to play off of my ‘Noob Mistakes’ article a bit here and guide you through the process of diagnosing issues with your hotend.  I’ll lay down some tips to help you prevent and repair some of the damage you may have caused with hotend jams.

Hotend’s Clogged!

Look through these causes to see if you can figure out the WHY of your hotend jam.  The best prevention of clogs and jams is Knowledge.  3D printing can be a daunting hobby at first, but don’t fret and hang in there!  The greatest thing about 3D printing is the community!  Yeah, that diagram was specifically designed for this article.

Cause: Too High of Retraction

I know, it’s a bummer.  Sometimes it’s unavoidable, but other times it’s pretty much completely your fault.  From watching users across the forums, I would say the number one cause of hotend jams is because of incorrect slicer settings.  With a typical PTFE lined hotend, your retraction should be set as so:

Of course, if you’re using an all-metal hotend divide those numbers in half.  All-metal hotends also require a slight bump in temperature.  The PTFE lining that is found in most hotends acts as a kind of lubricant for the filament when it is being retracted.  Since the all-metal hotend lack this PTFE lining, you can quickly cause hotend jams by using TOO MUCH retraction by pulling filament into the cold zone.  Refer to the above diagram for questions about cold/hot zones.

Cause: Dead or Failing Heat Sink fan.

No, I’m not talking about your parts cooling fan.  I’m referring to the fan that should be running whenever your hotend is heated.  If this fan seems to be failing or isn’t running at all, this is a problem.  Heat from your heater block will creep up into the cold zone of your hotend and cause jams.  You need to make sure that the fan is working, and that this area is cool to the touch.

Cause: Crap Components

I’m going to lump in cheap all-metal heat breaks and degraded PTFE liners into this one category.  Cheap heat breaks will give you all sorts of fits.  I used cheap ones for awhile and would always get random jams.  Since I have been running Micro Swiss all-metal heat breaks, I haven’t had a single hotend jam(with properly tuned retraction).  PTFE lining will soften at temperatures about 220c and sometimes issues can occur at lower temps.  It’s important to stay on top of this because even though it melts at a higher temperature, it can cause problems over time through use.  Remember not to print at high temperatures with your PTFE lined hotend!

Cause: Inaccurate Readings.

Also, keep an eye on your idle or cold temperatures.  The reading for your hotend and bed thermistor should be pretty close.  If you are noticing a pretty big gap when cold, that means it is also off when it’s hot.  If that’s the case, you could be running too cold or too hot.  Either way can cause jams, so it’s always a good idea to stock a spare thermistor to swap in for testing purposes.

Cause: Slow Removal of Filament.

So, you were trying to replace your filament and now.. you can’t force your new color through.  More than likely you jammed your hotend in the cold zone.  This happens when you are removing the half melted tip of filament too slowly and it literally cools before it leaves the hotend.  Next time, speed it up and don’t dilly-dally!

Removing the Hotend Jam

Alright, you’ve gotten a hotend jam.. so how do you remove it?  Well, that depends on how bad the jam is.  I’ll detail a few of the removal methods below:

Hotend is Clogged, Zero Flow

There’s a couple ways to remove a hotend jam.  I don’t recommend using special drill bits or anything like that to fit into the ACTUAL nozzle hole.  Those tend to just snap, and now you have filament AND a broken bit clogging your hotend.  Let’s not make this harder than it has to be.

The first is the most complicated, but most thorough.  I will just high light the general steps.  Depending on the type of hotend that you own, it may come apart slightly different.

The ‘Tear Down’

1. Remove as much of the filament as possible.
2. Heat hotend to printing temperature and then turn the printer off.
3. While the printer is still hot/warm remove and disassemble the hotend assembly sensors and heater.
4. Remove the nozzle and heat break.
5. Use a torch, oven, or boiling water to soften or burn away the plastic from the metal parts.
6. Assemble, but do so as I state in ‘Putting It All Back Together’!
7. Perform an atomic pull to remove any left over particles from inside the nozzle face.

The ‘Quick-N-Dirty’

1. Remove as much of the filament as possible
2. Heat hotend to slightly above printing temperature
3. Disconnect ‘cold zone’ fan
4. Use a 1.5-1.9mm wire to forcibly push the filament out of the nozzle.**
5. With the jam removed, reconnect the fan.
6. After that, Perform an atomic pull to remove any left over particles from inside the nozzle face.

**If you use a bowden style extruder, you will want to pull out the PTFE tube so you can try and push the filament directly through the nozzle. 

Hotend is SLIGHTLY Clogged, Causing Print Quality Issues

There are a few things that can cause what looks to be a partial clog.

• One is your PTFE tube if you are a bowden drive system.  Make sure that the tube is cut straight and inserted FULLY down into the hotend.
• Another thing to do is check out some of the common extruder problems that can look like a clog.  A dirty drive gear can give you headaches!

If filament will still push out of the nozzle, you may be able to do an atomic pull to clean the jam out.  Yes folks, this is the procedure that you’ve read about in ALL the groups.  I’ll be honest, I don’t know who coined it as the atomic pull.  Regardless of it’s name, it works.

The Atomic Pull

1. Heat up your hotend
2. Turn off the heater for your hotend
3. Start slowly manually pushing filament out of your hotend, just keep a constant pressure on the inside of the nozzle
4. When the temperature drops to around 150-160C, RIP the filament back from the nozzle and out of the hotend EXTREMELY QUICKLY!
5. Next, check out your filament tip after removing it from the hotend.  If done right, it shouldmbe perfectly formed like the inside of your nozzle.  Also, check for any foreign material in the tip of the filament
6. Repeat until the filament is clean.  If your filament tip isn’t coming out as defined as it should, you may have to let the hotend temperature drop a little lower than 150C.

Putting it All Back Together

So, you tore your hotend all apart and you want to reassemble it.  There’s a right way and a wrong way to do it.  When doing this the wrong way, you may not even notice any problems for awhile.  Not until you see something dripping down your heater block or from around your nozzle.  Make sure that the mating surfaces of the nozzle and the heat break are nice and clean.  After that, follow the below instructions for a leak free life:

1. Thread the nozzle into the heater block, but leave it so it has around 1mm of space before the face of the nozzle is tight on the block.
2. Next, thread the heat break into the heat block so it is TIGHT against the nozzle
3. Then, thread this assembly into your heat sink
4. After that, attach the thermistor and heater cartridge, be careful with the wiring.
5. Heat the hotend up to 150C and let it set for a bit.
6. Then, retighten the nozzle while holding the hotend assembly to keep it from spinning. DO NOT SKIP THIS!
   
7. Enjoy leak free printing!

Conclusion

Whew!  That’s a lot.  Hopefully you have everything figured out now to live your 3D printing life free from hotend jams!  There’s a lot of information in here, so go back and read it through a few times before performing any of these.  Are you guilty of any other common Noob Mistakes?  Check that article out and save yourself!

Have you ever calibrated your steppers?  If not, Check out our Stepper Calibration Guide!

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