P1S leaking from nozzle (not holding pressure?)

Bambu Lab P Series Troubleshooting
1

Today I had a nozzle clog in a P1S. Standard needle unclog didn’t work, so I did a cold pull which cleared the clog.

Since then, the nozzle constantly leaks filament if there’s any loaded in the hotend. I’m heating the nozzle to 250c as I would with a cold pull, but instead of the first line of filament being extruding, then stopping with the rest left in the hot end, it just keeps going. It’s much slower than intentional extrusion, but is sufficient enough to be a constant stream. If left alone with the nozzle heated, the hot end will completely drain and it will need several extruder activations to push enough filament back into the hotend.

I’ve disassembled both the hotend and the extruder. There was no noticable debris inside either, and the hotend is clear enough inside that I can see through it.

The extruder appears to be working exactly as expected, so I believe there is an issue with the hotend and/or nozzle.

Something of note is that usually when manually loading filament for a cold pull, I have to activate the extruder 8 times in order for filament to be pushed out the nozzle. At the moment I only have to do this 5 times, and the filament sort of spits/bursts slighty out of the nozzle. I’m assuming there is a pressure issue and as soon as filament enters the hotend it’s draining out of the nozzle.

As I test, I loaded some PLA at 250c by hand, changed the temp to 0c, then manually used the cutter and backed off the extruder to remove the loaded filament, leaving only what is in the hotend. By the time the hotend fully cooled and could be removed, there was nothing left inside.

I don’t have any spare P1S hotends on hand, so is there anything else I can try in the meantime? The nozzle has been heated and then cleaned with iso and a brass brush, is visibly clean and can be seen through, so I do not think there’s a debris issue. The hotend is securely seated in the correct position and is screwed in properly.

Maybe it’s just fully cooked? Could I have damaged it with the unclogging needle?

2

Well another nozzle is obviously the best answer. How old is this nozzle? What filament are you printing that you need to do so many cold pulls? I haven’t done one in years.

The reason I asked is I can’t remember ever being able to see through a .4 nozzle. I’m old though.

3

There is always cleaning filament

But frankly if you dont have a spare nozzle then you wont have that.

Overnight yourself a new one and dont worry about it.

4

Not old, couple hundred hours print time maximum. Only printed PLA, PETG, and TPU through this.

A while back (before this printer) I had a bunch of issues with contaminated filament, so I had to do a million cold pulls trying to isolate it. I’ve only done one cold pull on this printer, and that was today to clear the TPU clog.

5

I do have some cleaning filament (Though I’ve never found it particularly effective at anything), and gave that a run through, but it just acts the same as regular filament.

I need some spare hotends anyway so I’ll just get some, but I thought there might be something I could try as this nozzle is pretty new (Maybe 200 hours print time absolute maximum.

6

If it was tpu that caused the clog, dry it. I went rounds and rounds on weekend with TPU. Wouldn’t work until I dried it. Kept giving clogs until then.

7

It had been dried 24 hours prior to printing and was being actively dried while printing. I’m actually wondering if the hotend failed in some way and that’s why the TPU clogged.

8

So turns out I do have spare nozzles, just not spare complete hotends.

Took the existing hotend apart, and the wire pad just came away clean - absolutely no thermal grease underneath it at all.

Greased the new nozzle and put it together and back in the printer, but same issue occurring.

Presumably if the thermal grease was mssing the wires/thermistor may be damaged and the whole unit is fragged?

9

time is a flat circle; measure the spool to 0.1g, dry it, weigh it again, and do not stop until it stops

TPU dribbling out of your nozzle is exactly what TPU loves to do, and its 10 times worse when wet. What vendor/shore/flex profile?

10

That’s a real possibility. Using a metallic object in the filament path can damage the nozzle or hotend, so it’s best avoided. The behavior you describe is consistent with extruder slippage or filament tolerances being off. The extruder drive gears are designed to grip plastic only, not resist metal tools.

You’ll want to keep a spare nozzle assembly on hand regardless - these issues come up from time to time. If you haven’t upgraded your extruder yet, this would also be a good time to do so, and it will help with diagnosing the problem.

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Check the extruder teeth

In the meantime, while you’re waiting for your new nozzle assembly, inspect the extruder teeth for damage. This will help confirm whether the extruder is contributing to the issue.

Use a magnifier in the 10–15x range. Anything higher will narrow the field of view too much. A jeweler’s loupe is ideal, but handheld magnifiers also work. Examples:

Here’s what to check:

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image1536×1024 42.1 KB

There’s a good Wiki guide on replacing the extruder unit:

If you need to go deeper, see the clog-removal and extruder upgrade guide for full disassembly:

Warning: Do disassembly over a magnetic parts dish or inside a shallow casserole dish. The screws are tiny and very easy to lose. Ask me how I know. :flushed_face:

Reference video with full instructions: https://www.youtube.com/watch?v=CLlT1RV-oJE

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Manual assist extruder test

Another check is to manually feed about 12" of filament while running the extruder from the front panel. This lets you “feel” whether filament flows freely.

  1. Press the filament in while the extruder is active. If it flows smoothly, test again without manual pressure.
  2. Compare the two. If the flow changes, it points to worn or damaged extruder teeth.
  3. For testing only, raise the nozzle temp about 20°C above the filament’s max rating to confirm free flow. Do not run like this long-term - excess heat can cause heat creep and clogs.
11

So you followed this procedure, including dialing down the temperature.
P Series cold pull
Filament continuously melting sounds like heat still set high.

12

It was wet TPU.
Sounds exactly how that Sirya Tech TPU behaved. Dried it for 3 days before it would print. Same for BL. Just because it sat in hot air does not mean the spool dried.
What do I know…

1 Like
13

Ok so I’ve resolved the issue. Both the extruder and the hotend are totally fine.

I swapped the rebuilt hotend from the issue printer with the hotend from another P1S and manually loaded both, and BOTH started leaking from the nozzle. At this point the only commonality was the filament I was using. I tried some from a different spool and the issue immediately went away on both.

The issue filament was some BBL basic PLA, a couple metres of scrap I’ve kept on hand to test with. Apparently it’s degraded enough in some manner as to just leak out the nozzle.

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