Since most Bambu Lab printers are the same age, I can imagine
that this problem could affect several people here in the forum.
My printer has been producing imperfect prints from time to time lately.
After 3 weeks of vacation I wanted to use it yesterday and this is what I got as a result:
So I cleaned the nozzle according to the instructions and was in good spirits when the next print looked pretty decent at first glance.
When the printer stopped extracting filament after a few cm height (unfortunately no image), I cleaned the nozzle again.
But the following result wasn’t much better.
Then I remembered that I had already seen similar prints here in the forum.
So I removed the hotend and took a closer look.
The reason for the bad prints is so simple that it made me laugh:
The THERMAL GREASE had hardened.
There is a thin layer of thermal grease between the hotend and the ceramic heater for better heat transfer.
This was dry and crumbly.
So I cleaned the hotend, ceramic heater and thermistor with a dry sponge.
This was quick and easy. You just have to make sure that there are no remaining hard paste hiding in any cracks.
Then I applied fresh thermal grease (supplied with the spare parts).
More is better.
There are corresponding videos on the Bambu Wikipedia explaining how to do this.
Afterwards I had perfect prints again.