Nozzle Cleaning Failed (MK4, MK3.9)

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To achieve good quality prints, it is fundamental that the nozzle can make the right amount of contact with the print surface. In case this is not achieved, the Original Prusa MK4 or MK3.9 will show the message "nozzle cleaning failed". 

How to fix it

Nozzle cleaning

Check if the nozzle has residue. Debris on the nozzle or heater block can affect its thermal properties. To clean it, heat the nozzle for three to five minutes at 250 °C, as the remains of the filament must be warmed up slightly so that they can be removed more easily.

Use a small brass brush to clear away any old plastic stuck on the nozzle and heaterblock.

Caution: the printer is still at a hot temperature! Wait until the hot parts are cooled down to ambient temperature. It takes approximately 10 minutes. Do not touch it! Always check the values on the display.

Steel sheet cleaning

Make sure that the steel sheet is clean of any residue. For the smooth, textured, or satin sheet, clean with 90% or higher percentage isopropyl alcohol (IPA). 

Check if the nozzle is not loose

The nozzle on the Nextruder has to be at the correct height and tightened. To check this aspect, loosen the thumb screws (do not completely remove the screws, a few turns are enough) on the side of the heatbreak, and push the nozzle up. Tighten the thumb screws just by hand, do not use any tools. 

If you have a Nozzle Adapter, check the installation again to make sure that the nozzle has not been lowered or loosened with the installation of the adapter. 

Check the bolts that interact with loadcell 

Some of the Nextruder bolts, if too tight, might generate extra forces that can be sensed by the loadcell, skewing its readings, hence potentially causing the issue. Check if slightly loosening the following bolts, while having the parts still tight and secured in place, can solve the issue: 

1. Slightly loosen the two bolts holding the hotend fan. If this doesn't solve the issue, proceed to the next step. 
2. Temporarily remove the hotend fan by removing the previously adjusted bolts. This will expose the heatsink/loadcell. Then, loosen very slightly the three bolts that hold the heatsink/loadcell in place.