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What's causing these burn(?) marks?


Hey community!

Noticing that for my last two prints, I’m getting these little blotches of darkened material. Is this a burn mark? How do I fix this? It doesn’t appear often, but here and there!


You may want to check for filament seeping out between your hot end and the body of the extruder.

Another option is trying to clean out the inside of your nozzle. Try a few cold pulls and see if any contaminants are coming out. Your previous filament may have pieces stuck inside and your current filament may require a much higher temp burning the old stuff.

Sometimes its hard to watch but you may have extrusion issues where a blob is formed and gets pushed onto the nozzle tip and sits there until it burns and falls off.

Last. You may want to try a different temperature setting. You may have a different spool requiring a different temp setting than you are used to.

Its funny this is happening on a red/orange filament. That just happened with mine the other day.

My fix wasnt much. I did a few cold pulls, cleaned the outside of my nozzle, checked for leaks and finally just ran a print through that was a test.

Cleared up after that


Yeah the last time this happened, I was using red filament.

And I guess it has to do with the printing temp, because this happens mid-way through the print and not at the beginning. Not very sightly when we get to the top of the print and the surfaces gets these weird black splotches :frowning:

Okay, I may try lowering temperature a bit, as well as cleaning the nozzle! Thanks!


What brand is the red filament and what temperature are you at currently?


It’s PET+ by MadeSolid. I print at 240 degrees!


It looks like something is being spit-out occasionally, and randomly, and at different areas. (ie: PTFE liner)
Are you using an All-metal hotend ? (if yes, disregard the following)
240*C would be pushing the limits of a ptfe liner in a typical hotend, over a limited amount of print time.
It maybe be time to replace the ptfe liner, or just upgrade to an all-metal liner.
If you think is might be the case, let me know what printer brand and model you are using, and I’ll track down some links for replacement parts, and instructions.


Can you provide a very close up image of the marks? Could help with diagnosis by looking at the type of mark and area around it.

It more than likely is contamination introduced during printing (like a build up on the nozzle and then gets caught in the print which has already been mentioned) but I would also like to add another possibility to the mix in case others see similar issues. I once had a dodgy USB cable connecting my printer to PC and was causing the printer to pause occasionally, essentially waiting for commands, and once communication picked back up again away it went. Probably a rare case but it can happen.



Hey Gene,

We’re using an Ultimaker 2 in the office, and the hotend is metal! We recently did just replace the hotend though, so it seems strange that that would be the issue :frowning:


Hey Jason!

I painted over the frame last night, but realize I didn’t yet do the side with the splotches. Phew!

Here’s some closer up photos. They really just look like smudge marks, except not rub-offable:


What type of filament was loaded in previous to the PET+?

I would recommend getting this: I use this stuff to purge filament when switching from ninjaflex or pet+ to pla or vice versa because a cold pull doesn’t always seem to get everything out of the nozzle. I haven’t got any burns on any prints since I started using that filament when switching filaments types.


Oh wow that seems popular— sold out!

I believe it was also PET+, because we had just switched out the old nozzle (got impossibly clogged from wood infused filament), and we had put in PET+. If it wasn’t PET+ and my memory’s failing me, it might have been PLA.


PLA or the wood filament would make sense. Both are filaments that use a low temp. Going from one of those filaments to something that needs a higher temp to print without purging the previous material completely could cause those burn marks. At a temp over 210 C one is essentially burning the previous filament that is stuck in the extruder and nozzle and eventually it just leaks out randomly in blotches.


This might be pretty obvious but worth checking, you’re not over extruding or Z too low and getting excess stuck on the outside of your nozzle which is turning black and scraping off in parts of the print?


Check your roller wheels under the bed for accumulated white fuzz. When you get too much build up, pieces break off and go airborne. Your print has an electrostatic charge and it will attract these floaters. When the nozzle hits them, they burn easily and leave the brown splotches. Clean your roller wheels (all of them) with a vacuum brush. Problem solved.


I had this problem but even worse. Yesterday I found the problem; there was a load of PLA stuck to the outside of the extruder burning away (smelt bad), I think it got there when I had a print mess up and detatch from the base and the printer carried on splurging for a hours before I noticed. I removed all that c**p and now it works like a dream again.