New firmware 6.4.0 (MK4 and later), pure bliss!
Firmware update? Well, usually, we don't really notice the differences. It's usually the slicer that's where we expect the new features.
However, something has changed here, and for the better: the filament retraction in the extruder. That might not sound very impressive. But in practice, it makes a big difference.
Until now, to remove the filament from the printer, you had to select "Unload Filament." The printer would heat the nozzle to the filament's melting temperature, retract it, and then eject the filament from the top.If you didn't want to load another filament and shut down the printer, you had to go to Control/Temperature/Cooling to start the fan. Then wait for it to cool down before turning off the machine.
(Why remove the filament? To prevent burnt residue from accumulating in the nozzle.)
Now, after filament insertion and purging, the extruder retracts (displayed on the control panel).When you request to unload the filament, with the printer and extruder at room temperature, there's no need for heating. The extruder ejects the filament cold, smoothly, and very quickly. No need to wait to turn it off.
However, if you want to load a different filament, you'll obviously have to wait until it reaches the melting point. Makes sense.
Well, it might not seem like it, but it makes a difference. Because, whoever started unloading and, while it was heating up and expelling filament, did something else. Then forgot...? What was going on? The printer stayed at the melting temperature (230°C for PETG) until it got tired of waiting and sent a "heating off" safety message. Reassuring, but still not ideal.
MK4
RE:
Bliss??? Which printer do you have? 6.4.0 on the MK4S is a disaster. Ever since Prusa merged the 4S, XL, Core One, and Mini into one release we’ve been plagued with unexpected bugs. Whoever came up with that plan should have been fired. 6.2.6 was the last stable, unmerged, release for MK4S.
MK4S/MMU3
RE: New firmware 6.4.0 (MK4 and later), pure bliss!
That is a most excellent improvement.
That is meant to be my practice, but it is easy to forget that step and end up with a plug !
Now, after filament insertion and purging, the extruder retracts (displayed on the control panel).
RE: New firmware 6.4.0 (MK4 and later), pure bliss!
That is a most excellent improvement.
That is meant to be my practice, but it is easy to forget that step and end up with a plug !
Now, after filament insertion and purging, the extruder retracts (displayed on the control panel).
Yes, leaving filament in a hot end, especially low temp filament like PLA can cause nozzle clogs. Also, it helps with both filament changes and nozzle changes. It's a big improvement.
RE: New firmware 6.4.0 (MK4 and later), pure bliss!
I don't know about the MK4S, but for the MK4, this firmware works correctly.
Since the MK4 replaced my MK3S, I've seen continuous improvements thanks to software updates: initially, the MK4 would make a whining noise when it moved down to zero on the print bed. This issue disappeared with the newer firmware versions.
I had never tried printing with Flex or TPU, for fear of clogging the nozzle (bad experiences with PETG on the MK3S, so TPU was out of the question).
I gave it a go with Amazon TPU Basics and the profile integrated into Prusa Slicer. It printed perfectly on the first try, but since it sticks quite a bit, I used blue tape. Flawless.
OLYMPUS DIGITAL CAMERA 
OLYMPUS DIGITAL CAMERA 
Bliss??? Which printer do you have? 6.4.0 on the MK4S is a disaster. Ever since Prusa merged the 4S, XL, Core One, and Mini into one release we’ve been plagued with unexpected bugs. Whoever came up with that plan should have been fired. 6.2.6 was the last stable, unmerged, release for MK4S.
MK4
RE: New firmware 6.4.0 (MK4 and later), pure bliss!
I think most of the bugs are related to use of the MMU, so maybe you’ll never see them! Lucky you! 😁
MK4S/MMU3
RE: New firmware 6.4.0 (MK4 and later), pure bliss!
There's plenty of fun to be had with color without MMU. 😀 
MK4