PETG Fails Nozzle Cleaning every time.  

RE:

Did you chat with support? The nozzle cleaning is a part of the FW executing this command. So it can be also a load cell issue or it´s installation.  Do you have enough tided the screws holding the nextruder?

The textured sheet could have a problem, that the printer moves the head at different points to the same height. If the sheet is not smooth enough the load cell indicates different pressure and can result to the error.

This can be proven by the success with the smoot sheet.

RE:

it's most likley the textured sheet purge strip being worn down.  Smooth sheet prints every time.  Bad side of the Textured sheet (more purge tearout) only prints after a filament unload&load, and the other side of the Textured sheet prints 9/10 times without a nozzle cleaning failure.

Seems that they are sold out of textured sheets at the moment 🙁

So if you get the "Nozzle Cleaning Failed" message consider looking at your sheet..  May be time for a new one.  Hopefully the firmware team will make an option to probe for cleaning on the other side of the sheet.

RE: PETG Fails Nozzle Cleaning every time.

I want to add my findings to this thread.

I just got back from a trip and wanted to jump back into testing my XL-5. Found a good MM print and setup for PETG. Switched to the build plate with the rougher surface. Sliced and went to print and got the Nozzle Cleaning error. Tried manually cleaning the nozzle, tried removing the thermal sock, tried a whole bunch of things. Was getting frustrated. All the sensors that they added were supposed to make it easier to use, not harder!

Finally, I went back to PS and looked at my settings. Print quality was set to high with a very small layer height. I set that to speed with a much thicker layer height and the nozzle cleaning worked right away.

ALL my issues related to this machine have come from the Print Settings. Either these settings use a different printer's setup (which could easily explain SeattleDavid's battlebot problem) or the settings just don't work with some materials at all. I am finding that every time I slice a file I have to go into the "Print Settings" pull down menu and chose a preset or things sometimes just don't work. 

RE: PETG Fails Nozzle Cleaning every time.

OK, I have a workaround that seems to be working well.

It's a change to the Printer Start G-code to heat up the hot end, then cool it down.  My working theory is that a cold hotend doesn't deposit nozzle gunk on the sheet and dislodge it.

On my "Well Loved" textured sheet when printing from cold or nearly cold, one side will fail the Nozzle cleaning 90% of the time (Tried it 18 times, have 2 success). 
The following change has a success rate so far of 100% (6 tries).  Sample sizes are still small so appreciate feedback if you also have this problem.

RE: PETG Fails Nozzle Cleaning every time.

What are your Print Settings set to? Once I switched to a thicker layer height in the Print Settings Menu it worked perfectly.

RE: PETG Fails Nozzle Cleaning every time.

Tobycwood issue seems to be very different.  Layer height has nothing to do with the Nozzle Cleaning routine failing.  My settings were factory defaults with factory profiles. Fails exactly the same way regardless of layer height. 

RE: PETG Fails Nozzle Cleaning every time.

I completely disagree. The Layer height setting is coupled to the z offset which is used for all bed probing. Before I switched the setting I could see the bed come up against the nozzle much harder before the load cell activated. I switched to a “speed” setting in print quality and it worked right away.

Regardless, I’m finding just about everything that goes wrong on this machine is in someway connected to the Print Quality menu settings. I also had extrusion issues until I set the print quality to a preset. PS has a serious bug which is tricky to duplicate. It is not managing print settings correctly. in one case I found it used “Printer Settings” from another printer.

RE: PETG Fails Nozzle Cleaning every time.

Then we will agree to disagree.  Changing the Layer height makes no difference in the problem that I experience at all. Nor does the speed or print profile.  

Looking back at the files I have tested there is no statistical difference between 0.1, 0.15, or 0.2 layer heights with the failures.  In fact 0.2 has a more solid failure rate (10/18 failures are at 0.2, 1/18 is at 0.15, and 7/18 are at 0.1).  The 2 successful prints with the sheet in the "Correct" position, one is at 0.2, and one is at 0.1) and Also no correlation between speed or structural either.   The sample size is still small, but now out of  36 prints the odds of what I am seeing would be very unlikely to be related to either Layer Height or the preset print profile choices.  

I will re-state that I do not believe that you have the same issue as I have which is very clearly linked to an older textured sheet (specifically one side of it), where the Purge Line tear out occurs in the same area as the Nozzle Cleaning.  It's also comparing the your XL-5 which has a brand new sheet, to a MK3.9 with a very old and very used sheet. XL also has other differences.

I'm now at 10/10 success using the modified G-Code.  My hypothesis is that heating then cooling the nozzle prior to the Cleaning (within a few minutes) is much more successful at either softening the debris enough to dislodge or not matter in the initial probing process.  Since unloading and then loading was how I was first working around the issue, this narrows it down to being more related to the heating process of the Unload/Load than the retraction and re-feeding.

RE: PETG Fails Nozzle Cleaning every time.

I've also been struggling with nozzle cleaning failures on my MK3.9 printing with PETG. I did the upgrade last week and had a few successful prints after the upgrade, but lately I've been getting lots of failures - and could only get a print started after several retries. When it actually did get through the nozzle cleaning, I also had lots of prints where there first layer wouldn't stick correctly and would start peeling up and failing the print. Really odd - I never had these problems before the MK3.9 upgrade.

I tried using a brand new spool of PETG, thinking that the spool that I had been using for a week or so had absorbed too much moisture - but no difference.

I also tried the custom gcode above to heat the nozzle up to 230 and back to 170 - that seemed to help somewhat, but I still had a lot of failures.

Based on something I read in another thread, I updated to the 5.1.0-alpha2 firmware and PrusaSlicer 2.6.1 that was just announced, and I think it's fixed my issues? I resliced my object, started a print, and it seems to be good? It got through nozzle cleaning after printing maybe a half dozen 'dots' - then printed a great first layer with no peeling. Time will tell if this is really a permanent fix...

RE: PETG Fails Nozzle Cleaning every time.

Well through 2 prints after applying the 5.1.0-A2 Firmware update It's certainly helping! It's looking better but I haven't had time to print more than 2 things.
First print worked (without the start code modification).
Second Print failed partially, aka the first cleaning failed, but the second succeeded.

Time will tell, but this is good news.  Hopefully there will be a way to choose where on the sheet it cleans.   

RE: PETG Fails Nozzle Cleaning every time.

I also had this problem with PETG, but increasing the initial nozzle temperature to 215 degrees fixed the problem on 3 out of 3 tries. It looks like the default initial temperature of 195 degrees works for PLA, but someone pointed out that in the 5.0.0 FW the initial temperature doesn't change with the filament type. So, if the initial temperature is 25 degrees less than the first layer nozzle temperature for PLA, it needs to be 215 degrees for PETG. I just used the "Tune" option to change the nozzle temperature after starting printing.

Btw, I use a textured sheet and haven't experienced any problems in that regard. 

There's also a discussion thread on this subject in the Original Prusa Mk4 section:  "Nozzle Cleaning Failed." Error - Page 2 – Hardware, firmware and software help – Prusa3D Forum

RE: PETG Fails Nozzle Cleaning every time.

@SteveE Thanks for the hint, this fixed it for me. It would be nice if Prusa fixed/changed those Temperature Presets in the next Release.

RE: PETG Fails Nozzle Cleaning every time.

I have the exact same problem. Came with 5.0.0 on my MK4

Never had any issues really with the printer, all of the sudden i get error on nozzle cleaning 1-3 times in a row. I have to manually remove a blob it makes and then lower the temp manually.

Im looking into changing 
M140 S[first_layer_bed_temperature] ; set bed tempM104 T0 S{((filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : (filament_type[0] == "FLEX" ? 210 : (filament_type[0]=~/.*PET.*/ ? 195 : 170)))} ; set extruder temp for bed levelingM109 T0 R{((filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : (filament_type[0] == "FLEX" ? 210 : (filament_type[0]=~/.*PET.*/ ? 195 : 170)))} ; wait for temp

to 

M140 S[first_layer_bed_temperature] ; set bed tempM104 T0 S{((filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : (filament_type[0] == "FLEX" ? 210 : (filament_type[0]=~/.*PET.*/ ? 170 : 170)))} ; set extruder temp for bed leveling

M109 T0 R{((filament_type[0] == "PC" or filament_type[0] == "PA") ? (first_layer_temperature[0] - 25) : (filament_type[0] == "FLEX" ? 210 : (filament_type[0]=~/.*PET.*/ ? 170: 170)))} ; wait for temp

If i change the temp manually to 170 i have clear beginnings all the time.

RE: PETG Fails Nozzle Cleaning every time.

I still have the same problem. Out of 3 attempts it fails twice. Seems like Prusa does not understand the problem, when they are not able to fix it for half a year. I use Prusament PETG.
With my mk3s I can start the print and come back 2 hours later when the print is done. With the mk4 it's impossible. I have to come back 5 minutes later, check, retry, retry again and hope. I don't understand the benefit of this stupid not working nozzle cleaning function. The Mk3 doesn't have it and works very well.

RE:

PETG will coat the nozzle. This has to be manually cleaned off before you try to print. It has to be removed or it will inhibit accuracy for the load cell sensor. Prusa’s approach to this is far from optimal. However, all one has to do is heat up the extruder that, take it out of its parking place manually and wipe the nozzle clean with a paper towel. Please do not use a metal brush for this. It will damage your nozzle.

RE:

It also happens when I clean the nozzle right before start. It does not even seem to have an impact of the result. 

RE: PETG Fails Nozzle Cleaning every time.

I've found an easy solution: Take a sheet of printer paper and put it under the extruder during the cleaning, pulling it gently outward as the nozzle touches down. After a few touches like this, the cleaning succeeds. 

I initially thought the cleaning was just crazy, as I thought it was referring to the nozzle being blocked, which it clearly wasn't, having recently printed fine and possibly having had the filament changed and purged successfully. Finally I realized it instead has to do with crud on the face of the nozzle, so the abrasion from moving paper likely does clear something off. I often paint the nozzle with plastic repellent paint to help avoid PETG globbing, and perhaps that contributes to the problem. I don't understand what the MK4 is looking for, exactly--perhaps a change in extruder height when crud comes off?

This had become a big time waster, but this trick is a reliable workaround.

RE: PETG Fails Nozzle Cleaning every time.

thanks for the idea but I look more for a solution than a workaround. My mk3 just prints reliable after pressing start and I only have to come back for picking up the finished print. I use it for business and don't have the time to play around with it. For me the mk3 is the better printer. 

RE: PETG Fails Nozzle Cleaning every time.

I am pretty annoyed as well for this feature which I am not sure what problem is trying to solve. I have been printing PETG for 4+ years on my MK3 without any issue, not sure why the new FW has to do it. Moreover, it increases the total printing time considering I have to mess with the nozzle cleaning, push "try again" a few time, clean manually the nozzle and so on. I have been using on and off the MK4 for 2 months now and I am not satisfied.....MK3 still prints better and more reliably up to now