Hotend fan not spinning
I got this error and a failed print. Did the print failure cause the error? i.e. print failed and a bit of filament got into the fan. Or did the fan not spinning cause the failed print? The fan was always spinning just noticeably slower. I did find a strand of filament in the fan blades. After I removed it the fan did spin faster. (I have a video of the fan spinning before I removed the debris if anyone is interested.
1. How do I make sure the fan is totally debris free?
2. This is Polymaker PLA, fresh out of the dryer. So the cause is not wet filament. Also, I used a little bed glue, it is not an adhesive problem. I am printing with Prusa 0.4mm hardened nozzle and the Generic filament profile. All settings are default. These were going to be gridfinity bins.
Prusa Core One
There have been reports of false positive detection in this area - I've never encountered them - but if there was filament/dust/stringing debris in the fan interfering with rotation then it was a true fault report so working as expected.
The fault will trigger if the fan is running slow, not just stopped, as reduced cooling leads to poor print quality.
Make cleaning the fans part of your regular maintenance - not just picking out wisps of stringing (and cobweb, surprisingly problematic) but also clean dust from the blades and every couple of years open the back and put one drop of light machine oil into the hub. DO NOT try to clean the dust out with a vacuum or a blower.
Cheerio,
RE: Hotend fan not spinning
1. How do I make sure the fan is totally debris free?
Hi Phil
Long tweezers can normally take care of any tangled filament hairs that end up there. I also have an air compressor I blast it and the other fans out periodically (and the more gentle air puffer for regular times).
Worst case it's thankfully a somewhat easy part to access to replace. Does it turn freely with your finger?
Cheers, Geoff
RE: Hotend fan not spinning
Every 6 months (which is twice so far). I remove the Nextruder, completely disassemble it and clean it. This includes removing all grease from the planetary gears and relubing.
RE: Hotend fan not spinning
I used a can compressed air and lots of crap flew out of the fan. Surprised me how much came out. It is printing now, but looks like some stringing. 
Prusa Core One