Nozzle constantly clogging with PLA/TPU - Wrong GCode?

Bambu Lab H2 Series
1

Hello,

this configuration works perfectly on my H2D:

  • :white_check_mark: Multi-material print: PLA in left extruder, PLA in right extruder
  • :white_check_mark: Single-material print: PLA in left extruder
  • :white_check_mark: Single-material print: TPU in right extruder

However, multi-material prints with PLA in the left extruder and TPU in the right extruder are a complete nightmare – the TPU extruder clogs consistently, either immediately or after just a few lines.

What I’ve Tried So Far:

  • Performed a cold pull
  • Installed a brand-new nozzle for TPU
  • Switched to a low-friction Bowden setup
    → Hardware-wise everything seems fine

Investigation:

I noticed that the Generic TPU profile uses a very high nozzle temperature (240 °C). In contrast, the Bambu TPU 95A profile uses 230 °C and overwrites retraction with:

filament_retraction_length = 2
filament_retraction_speed = 10

Print Scenario:

My print starts with a large PLA section. After a few minutes, it switches to TPU – and that’s when the clog happens.

When inspecting the nozzle afterward, it seems like the filament gets too soft too high up in the hotend, possibly due to residual heat. I’ve used ERYONE 95A TPU for years without any issues, so I don’t believe the filament is the problem.

Suspicious G-Code Behavior:

In the Filament Change G-Code in Bambu Studio, I noticed that both hotend cooling fans (Extruder 1 and 2) are turned off with:

M106 P1 S0
M106 P2 S0

But I can’t find where or when they’re turned back on – especially in the TPU handling section.

Also, I’m missing a cooldown command for the previous extruder. Something like:

M104 T<old_extruder> S160

Might it be possible that the TPU fan doesn’t get reactivated properly, or that the standby temperature stays too high?

Does anyone have a suggestion or similar experience?
Any input would be highly appreciated!

Thanks! :folded_hands:

2

At this point, I’m still unsure which specific cooler is controlled by M106 P1 and M106 P2 , since the G-code contains inconsistent values and comments.

M106 S0 ; turn off fan
M106 P2 S0 ; turn off remote part cooling fan
M106 P3 S0 ; turn off chamber cooling fan
M106 P1 S0
M106 S255 ; turn on fan to cool the nozzle
M106 S0 ; turn off fan , too noisy
M106 S255 ; turn on fan to cool the nozzle
M106 S0 ; turn off fan , too noisy

I was wondering if there’s any kind of official documentation or wiki that explains the Bambu Lab-specific G-code commands?

Has anyone tried setting a specific cooldown temperature using M104 during filament changes?

Thanks a lot! :blush:

3

Are you heating your TPU from a dryer while printing by any chance?

4

I’m using a SUNLU S4 filament dryer to properly dry the filament before printing. The TPU is stored in a sealed dry box, and I’ve always had excellent print quality on various printers without any issues.

From my experience, the filament itself isn’t the problem. My theory is that the TPU sits heated for several minutes before it’s actually used, which causes the heat to creep up into the filament path and soften or weaken the material, eventually leading to clogs. But that’s just my personal theory — I could be wrong.

5

TPU expands quite a bit when heated and drying it while printing will cause problems. You need to dry it before printing, not during.

6

Aside from the annoying filament path changes and modifications, the H2D is pretty good with TPU. I’ve not had any issues with it, however, I don’t use the “Generic Profile”. There was a bug in it, that was clogging/partially clogging. Not sure if they fixed that yet, because I’ve never tried the Generic profile. Some YouTuber recently mentioned it in their H2D review.

So first off, I would suggest using the Bambu Profile and modifying it to match what you want. From what I’ve heard about the problem, the numbers and settings look fine on the Generic Profile, but it still clogs. However, switching to Bambu’s profile makes it run fine.

1 Like
7

Thank you very much! The bug in the “Generic TPU” becomes quite clear when comparing the files directly. The “Bambu TPU 95a” definitely seems much better, and I’m definitely planning to try it out.

I personally haven’t had any issues printing with TPU alone in the H2D. The clogging only happens when switching from PLA to TPU. Have you successfully printed parts using both PLA and TPU?

Also, which TPU brand or type do you use?

Thanks again!

8

Thank you much for your input! I always dry the TPU before and not during printing.

9

No problems in single or multi-material, most of my TPU printing is with other filaments (mostly PLA). The only issue I had was on the previous firmware, where it had an odd purge cycle in the middle rear of the build plate during multi-material prints. However the new firmware fixed that (even though it wasn’t on the release notes). So I’m guessing it was a corrupted file.

1 Like
10

I haven’t tried TPU on my H2D yet, but I do run my AMS HT in heating mode on the X1 Carbon while printing — zero issues there, aside from the minor “problem” that the print quality is noticeably better when I dry the filament during the job :grin: