H2D Dual toolchange forces inactive nozzle to 60°C – causes PETG stringing

Bambu Lab H2 Series
1

Hello,

I’m using an H2D Dual (0.4mm) with 2× AMS and Bambu Studio 2.5.0.66.

Since 2.5.x I’m experiencing the following behaviour:

During every toolchange, the inactive nozzle is forced to heater OFF via:

M104 T? S0 ;Multi extruder pre cooling

This causes:

• Nozzle temperature dropping to ~60°C
• Reheating from 60°C → 240°C before the next activation
• Pressure spike inside the melt zone
• Immediate filament ooze when the nozzle opens
• Stringing before reaching the purge tower
• Contaminated purge tower bottom

I tried:

  • Adjusting filament_pre_cooling_temperature in filament JSON

  • Setting large delta values (80°C for 160°C standby target)

  • Modifying change_filament_gcode template

  • Editing printer templates

  • Overriding standby temperature manually

However, Studio still injects:

M104 T? S0

after toolchanges.

This behaviour might work for PLA, but for PETG (240°C) in dual mode it causes consistent stringing and purge tower defects.

Questions:

  1. Is this forced heater-off behaviour intentional for H2D Dual?

  2. Is there a way to disable hard pre-cooling to S0?

  3. Can we define a true standby temperature (e.g. 160–180°C) for the inactive nozzle?

  4. Was this different in 2.4.x?

For dual PETG printing, a configurable standby temperature instead of forced heater-off would significantly improve toolchange behaviour.

Thanks in advance.

2

Considered drying your filament?

1 Like
3

That has nothing to do with it. Whether it’s dried or not.

4

Isn’t 60c below softening temp?

5

You think that oozing may not be caused by moisture? That is new to me.

I am sometimes having your behavior, and drying the filament resolves it.

It’s worthwhile trying.

6

This does not change the fact that after switching, the temperature of the unused extruder is set to S0 and thus drops to 60 degrees. Then, shortly before switching, it is heated back up to 240 degrees, creating high pressure in the nozzle. This is how the thread is created. A standby temperature setting of around 160 degrees is missing. And when it is heated to 220 degrees and then opened, it is almost gone. I have now changed this in the template and it works. But something like this should be included in the program.

7

You can adjust it however you want, but that won’t change the S0. It stays there.

8

lol@ giving yourself the solution.

1 Like
9

Surely I understand your question and reasoning, but I am just trying to help here.

I worked at support long enough to know that what customers think is the issue, or what they are asking for, is not always the cause of their issue.

Surely an issue can be resolved in many ways, but it definitely helps to take the simplest solution.

My question still doesn’t mean that your issue is moisture related, that is why I am asking. But just simply ignoring it as a possible solution is your choice.

The cooling of the nozzle to 60C just means that the PETG is cooling along with it. Why would re-heating it to printing temperature suddenly give it so much more volume than what it had before it cooled down?

Have you considered the fact that a wrong retract/de-retract might also be a cause for this issue?

I am even wondering why you posted a question and basically already decided that you had the answer/solution yourself.

It looks more like a statement now.

10

That is good for your stats :grin:

1 Like