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Core One +: Auto Vent opening  

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Andhrimnir
(@andhrimnir)
Member
Core One +: Auto Vent opening

If I have been informed correctly, currently the printer will only open/close the vent when you change/insert filament. This means if I am using PETG, it will open it once when I insert the filament and I have to leave the vent open. This leaves the printer open for dust/fluff/animal fur to enter the printer unecessarily while not printing.

  1. Is there any way to get it to open/close the vent before every print?
  2. Is there any way to get it to close the vent automatically after a print?
  3. If no to the above, how do I post it as a suggestion for future firmware updates?
Posted : 10/01/2026 11:44 pm
FoxRun3D
(@foxrun3d)
Illustrious Member
RE: Core One +: Auto Vent opening

See hyiger's gcode modifications in https://forum.prusa3d.com/forum/prusa-core-one-hardware-firmware-and-software-help/core-one-ventilation-grill/

Formerly known on this forum as @fuchsr -- https://foxrun3d.com/

Posted : 11/01/2026 2:52 am
hyiger
(@hyiger)
Noble Member
RE:

Since then I've moved it to a different spot. So now it's here which is a little earlier in the heat-up sequence

Start G-Code

{if chamber_minimal_temperature[initial_tool]!=0}
M870 C ; close vent
M140 S115 ; set bed temp for chamber heating
{else}
M870 O ; open vent
M140 S[first_layer_bed_temperature] ; set bed temp
{endif}

M109 R{((filament_notes[0]=~/.*MBL160.*/) ? 160 : (filament_notes[0]=~/.*HT_MBL10.*/) ? (first_layer_temperature[0] - 10) : (filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : (filament_type[0] == "FLEX") ? 210 : 170)} ; wait for temp

M84 E ; turn off E motor

G28 ; home all without mesh bed level

{if chamber_minimal_temperature[initial_tool]!=0}

End G-Code

{if layer_z < max_print_height}G1 Z{z_offset+min(max_layer_z+1, max_print_height)} F720 ; Move print head up{endif}

M870 C ; close vent
M104 S0 ; turn off temperature
Posted : 11/01/2026 3:06 am
Jürgen
(@jurgen-7)
Noble Member
RE: Core One +: Auto Vent opening

Can the M870 command be used before homing (G28)? Is the firmware smart enough to do a quick low-precision homing implicitly in that case, to get its bearings? 

Posted : 11/01/2026 7:19 am
hyiger
(@hyiger)
Noble Member
RE: Core One +: Auto Vent opening

 

Posted by: @jurgen-7

Can the M870 command be used before homing (G28)? Is the firmware smart enough to do a quick low-precision homing implicitly in that case, to get its bearings? 

Yes, M870 will home when the home position is unknown 

Posted : 11/01/2026 8:09 am
2 people liked
iftibashir
(@iftibashir)
Noble Member
RE: Core One +: Auto Vent opening

I haven't upgraded my system to the + yet, but I assumed it would open/close the vent before/after each print by default. I thought that was the whole point! I tend to leave a single filament loaded for a long period and may just use the printer with that one filament now and then - I don't change very often as I have another multicolour printer anyways - so my Core One will be powered on/off when needed and the filament kept loaded. 

So do you mean by default it only opens and closes the vent when loading/unloading filament and not before/after actual print jobs?

If so, I'll be using the above GCode too! 

Click here for VIDEO BUILD GUIDES + 3D Printing Tips!

--> Core One - MK4 - MK4S - MINI+ - MMU3 - Accelerometer Guide <--

Posted : 12/01/2026 9:06 am
Jürgen
(@jurgen-7)
Noble Member
RE: Core One +: Auto Vent opening
Posted by: @iftibashir

I haven't upgraded my system to the + yet, but I assumed it would open/close the vent before/after each print by default. I thought that was the whole point! I tend to leave a single filament loaded for a long period and may just use the printer with that one filament now and then - I don't change very often as I have another multicolour printer anyways - so my Core One will be powered on/off when needed and the filament kept loaded. 

So do you mean by default it only opens and closes the vent when loading/unloading filament and not before/after actual print jobs?

If so, I'll be using the above GCode too! 

The default behavior is that the firmware opens/closes the vent before printing, depending on the filament type. But it also remembers the last state and does nothing if it thinks the vent is still in the right position -- so if you closed the vent manually in the meantime, you are out of luck. And it does nothing after printing. 

I am still using my original vent automation; don't see a need to implement the "+" changes since they will become redundant with the INDX upgrade anyway. Its Gcode sets the right state before every print, and closes the vent afterwards. Hyiger's code above does the same, but uses the new M870 command instead of explicit move commands.

Posted : 12/01/2026 9:14 am
2 people liked
MarvinCZ
(@marvincz)
Member
RE: Core One +: Auto Vent opening

 

Posted by: @iftibashir

I haven't upgraded my system to the + yet, but I assumed it would open/close the vent before/after each print by default. I thought that was the whole point! I tend to leave a single filament loaded for a long period and may just use the printer with that one filament now and then - I don't change very often as I have another multicolour printer anyways - so my Core One will be powered on/off when needed and the filament kept loaded. 

So do you mean by default it only opens and closes the vent when loading/unloading filament and not before/after actual print jobs?

If so, I'll be using the above GCode too! 

It also runs if the printer was powered off, not just for a filament change, so that should cover your scenario.

Posted : 14/01/2026 2:03 pm
hyiger
(@hyiger)
Noble Member
RE:

 

Posted by: @marvincz

 

Posted by: @iftibashir

I haven't upgraded my system to the + yet, but I assumed it would open/close the vent before/after each print by default. I thought that was the whole point! I tend to leave a single filament loaded for a long period and may just use the printer with that one filament now and then - I don't change very often as I have another multicolour printer anyways - so my Core One will be powered on/off when needed and the filament kept loaded. 

So do you mean by default it only opens and closes the vent when loading/unloading filament and not before/after actual print jobs?

If so, I'll be using the above GCode too! 

It also runs if the printer was powered off, not just for a filament change, so that should cover your scenario.

It won't cover the case where the vent state becomes unknown between prints. Like you accidentally open or close it which happened to me enough that it was ruining prints. 

Posted : 14/01/2026 6:39 pm
iftibashir
(@iftibashir)
Noble Member
RE: Core One +: Auto Vent opening

Tried the above G-Code after adding the vent opening pieces and its worked perfect. Thanks @hyiger ! 

Click here for VIDEO BUILD GUIDES + 3D Printing Tips!

--> Core One - MK4 - MK4S - MINI+ - MMU3 - Accelerometer Guide <--

Posted : 22/01/2026 10:13 am
iftibashir
(@iftibashir)
Noble Member
RE: Core One +: Auto Vent opening

Only thing I may change is when the closing sequence runs. 

At the moment with the above GCode the printer finishes its print, the vent auto-closes and the printer then cools down. 

Makes more sense to me if the printer cools down with the vent in the open state for some external air, and then closes once the cooldown process has completed.....?

Click here for VIDEO BUILD GUIDES + 3D Printing Tips!

--> Core One - MK4 - MK4S - MINI+ - MMU3 - Accelerometer Guide <--

Posted : 22/01/2026 10:15 am
FoxRun3D
(@foxrun3d)
Illustrious Member
RE: Core One +: Auto Vent opening

Wouldn

Makes more sense to me if the printer cools down with the vent in the open state for some external air,

But to do that wouldn't you have to replace the M104 and M140 codes with M109R and M190R to wait until hotend and bed have cooled down before closing the vent? Which wouldn't be great for impatient guys like me who rip the sheet out of the printer as soon as the print is done 🙂 

Formerly known on this forum as @fuchsr -- https://foxrun3d.com/

Posted : 22/01/2026 12:51 pm
hyiger
(@hyiger)
Noble Member
RE: Core One +: Auto Vent opening

 

Posted by: @iftibashir

Only thing I may change is when the closing sequence runs. 

At the moment with the above GCode the printer finishes its print, the vent auto-closes and the printer then cools down. 

Makes more sense to me if the printer cools down with the vent in the open state for some external air, and then closes once the cooldown process has completed.....?

I thought about that as well, however for filaments that require the vent to be open the chamber temp is only around 30-35° in my case so doesn't really make much difference in the end. To make that change do something like the following. I'm very far away from my printer to test this but I'm not sure if M190 R0 stop when the bed is at ambient room temp or it waits forever? 

M104 S0 ; turn off nozzle temp
M190 R0 ; wait for bed to reach 0? or ambient? wait for eternity? don't know...
M870 C ; close vent 
Posted : 22/01/2026 2:06 pm
iftibashir
(@iftibashir)
Noble Member
RE: Core One +: Auto Vent opening

Considering what @FoxRun3D mentioned above - I'm probably the same. After a print the door is opened to grab the print anyways and now that I think of it, I used to manually close the vent before the cooling had completed regardless. Best not make an issue out of nothing I guess! lol

Click here for VIDEO BUILD GUIDES + 3D Printing Tips!

--> Core One - MK4 - MK4S - MINI+ - MMU3 - Accelerometer Guide <--

Posted : 22/01/2026 2:27 pm
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