MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking  

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

From the GitHub issue:

FYI: The fix will be included in the next firmware release. Please understand that testing of new firmware takes a while. The MMU can be used on the MK3.5/S, MK3.9/S, MK4/S, CoreOne and CoreOne L so testing all these possible combinations takes a while.

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

This is still happening in 2026.  Glad I found this post.  Will try and downgrade to the earlier FW.  I wish I could get the filament back that I've wasted trying to get this print to complete.

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

Posted by: @dbv

From the GitHub issue:

FYI: The fix will be included in the next firmware release. Please understand that testing of new firmware takes a while. The MMU can be used on the MK3.5/S, MK3.9/S, MK4/S, CoreOne and CoreOne L so testing all these possible combinations takes a while.

That posting was from months ago with no indication of when to expect a new release.

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

Glad I found this… I’ve been having the same issues and its been driving me mad.

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

So I hate being the new guy and ask a question that’s probably been asked a thousand times before…but I’m not having much luck searching for an answer.

How do I change my firmware BACK to an earlier version as some of you guys have recommended?

RE:

@martinij77
Here is a help doc that should give you the info you are looking for;

https://help.prusa3d.com/article/how-to-downgrade-firmware-core-one-mk4-s-mk3-9-s-mk3-5-s-xl_725930

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

Thanks Dude!

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

I had this issue today, had it in the past but it stopped happening. I noticed it only happened with one slot of the MMU3, not the others, and also saw that it purged a bit of filament before the wipe. This was with filament already loaded to the nozzle. I tried selecting yes to unload filament, even though it was the right one, and then I noticed it was set to the wrong filament type in the MMU setting. Changed that, works perfectly now.

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

Do we know if this bug was fixed in the latest beta firmware 6.5.3?

RE: MK4S +MMU3 + 6.40 Alpha FW - Stuck at Reloading Filament - 99% Parking

For God's sake, if you are using an MMU unit, never, I repeat never start printing with filament loaded into the nozzle! Have the filaments ready in the correct MMU slots and let the MMU load the filaments according to the settings in the slicer! The unit is not stupid and will know how to load the filaments!