At first I thought it was a one off - but now its happened 4 times with different PLA filaments. The problem appears to be when the print has finished and the filament is to be retracted back into the AMS from the right hand nozzle. The filament gets broken about 2 inches into the feed tube above the nozzle. Once the tube is removed from the head the filament can be pulled out so its not stuck in the head gears - any ideas? Filament is Bambu PLA basic - humidity in AMS is 34%. Nozzle is standard 4mm.
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wet filament is brittle. dry your filament.
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34 Percent is konsidered wet…
I start a dry run over night as soon as it reaches 20 Percent.
Check your Filament and discard the outer layers, old and wet pla probably wont come back from a brittle state
Over-dried PLA can also become brittle and prone to breaking.
Both moisture-saturated and over-dried PLA are problematic, as they can lead to poor print quality due to degradation of the polymer chains. Maintaining optimal moisture levels is key to preserving the filament’s mechanical properties and printability.
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Many thanks for the advice. I have the new AMS 2 - any idea what percent humidity I should be aiming for with standard Bambu Labs PLA sitting in it?
<15%. at least <20%. and if it breaks easily it’s because your filament is already very wet.
all my amss are <15% constantly (i used lots of silica beads).
you won’t overdry your pla by keeping the relative humidity low. you would only overdry it by baking it too many times.
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Humidity in the AMS says little about the condition of the filament, but if the material breaks easily, drying would at least be my first approach.
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Many thanks for the information guys - its appreciated. - I’ll start the drying cycle today 
All three of mine are currently showing below 10% RH, while the older ones used for my X1 Carbon are at around 11% at the moment.
Keep in mind that RH sensors respond slowly to changes, so if the lid has been opened recently, it may take a while before the reading stabilizes. The moment you open the lid, the displayed value no longer reflects the actual RH inside the AMS.
As already mentioned, the RH value doesn’t indicate the filament’s dryness directly—it only shows the humidity inside the AMS, which can suggest whether your silica gel needs replacing.
I am having the same issue.
What I have noticed is when it is a multi-color print where it changes regularly it never breaks. Now when I do a light box, where once the face plate has finished and then goes on to do the walls, the last color loaded in the right nozzle just sits there until the print is done which can be a couple hours as the left nozzle is loaded with black. Consistently the color that unloads once the left nozzle is done printing breaks and throws an error with 99% finished which is just the unloading process then it’s done.
Doesn’t matter if the filament is dried, new, open roll or whatever. It has something to do with it sitting idle for a longer period of time and I would consider it a problem/fault. Not a huge one but it is a pain when it breaks every time and you have to remove the PTFE from the extruder to remove it. As the person stated that started this thread, its about a 2" piece.
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It is exactly what you mention.
Due to the fact that the filament just sits there and doesn’t move, but the PTFE tube is constantly in motion at the relative sharp bend into the tool head, the filament breaks there.
I don’t know if it was CNC Kitchen or Vector 3D that mentioned this in one of his reviews. I believe there is already a feature request to retract the unused filament when it is not required for a long time. Of course that must be in an AMS to do so.
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Good point about the filament not being withdrawn. I was using printing from the left nozzle with a second colour briefly used in the right one - so it stayed there for the duration of the print - maybe that is the problem.
I have 2 H2D printers and yes I am gwtting the same issue. my printers have 2 AMS Pros attached and when doing multi collor prints the right nozzle brakes the filiment evey time. I think bambu should give us the option to unload filement after a layer number then we could manuly unlode it after we are done with the right nozzle.
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I am having the same issue. Never a problem with my X1C with the same roll of filament. But the H2D is breaking every print. Insane.
It breaks under idle for a longer period of time as well.
Also having this issue but with HIPS / Support for ABS loaded in the right nozzle. 2 rolls of support for abs and an off brand HIPS. All dried via bambu HT AMS.
I don’t trust AMS HT as a dryer, dry it with proper dryer
I’ve just come across the problem. My print is almost entirely one colour, left nozzle. However, there is a little bit of colour from the right at the start, and then a different one again many hours later. Every single time the filament that needs to be retracted after hours of not being used snaps. It seems to usully be about 5 cm (2”) or so above the extruder.
Initially I thought it was older filament, though it wasn’t that old. However, it’s happening with brand new Bambu filament (first print) that was also dried correctly (separate filament dryer), so its not a filament drying issue or similar, and I’ve never had a filament break yet other than under this situation.
Also, like someone else mentioned, it isn’t a problem with my X1-C … which makes sense as the filament not being used won’t sit there like with the H2D.
At least, thanks to here, I now know why. I did suspect it might be this but now know for sure.
Has anyone heard if they are any closer to fixing this? The siolution, as mentioned above, seems fairly simple.