Error FR0121 CFS filament in use, please retract filament

Flagship K Series Creality Flagship K2 Plus & CFS
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HI All,
Thought I would note how the following error appears when in truth it should be impossible.

Conditions:-
a) CFS connected to K2 but only reel 3 loaded with filament. CFS display confirms this.
b) Load external spool and extrude
c) Send print to K2 to print from external spool.
d) 3 hrs into print an issue developed so I pressed pause
e) decided to abandon and so retracted external spool filament
f) Pressed stop.

Pressing stop is fundamentally what causes the above error and is repeatable. Whether you use the CFS to print or not. However the error DOES NOT APPEAR until you next print :frowning:

The reason is that the system does NOT clear out the current printing information from machine management and therefore it thinks you are still printing from the CFS - even if you, like me, are printing from external spool.

Following the above I sent a new print (same model) to the K2.
Then the error appears, Pressed OK, so I disconnected the CFS.
You get the “no communication” error ( FS2831) pop up and pressed OK.
Reloaded filament from External spool and extruded such.
Resent the print model to the K2 to print.
The K2 display still showed the situation when I stopped machine. Like wise in the CP6 device page.
This display then changed when the actual printing started to the correct print situation

As you can see there is an underlying error handling routine not captured by the software team; hopefully this will be addressed in the new Chinese year.

If any one has come across this with abandoned print then please add to the post so developers realise it is urgent.

Summary,
Print from external spool, CFS not used
Stopped print causing CFS error but does not appear until next print

BTW if you do try and retract the filament at the error stage it just causes spool to revolve as there is not filament in the system.

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Is there an Error number related to the error? I would list it in post to have others who had to manage it informed as well. In Error history you see only the error numbers…
Anyhow, as far as I know there is a filament sensor in CFS (on this bottom 4 spools to 1 printer output multiplexer) which is failing - or getting dirty - for many users. This generates then an error that CFS is not in a clean retracted state.

If you print long time with spool holder you can avoid it (this error) by disconnecting the cable from CFS which comes from printer (before you power on the printer). Then it would work just with spool holder and the CFS cannot generate errors. I had to do that once waiting for a spare part as well.

Youl may need to contact Customer Service to get instructions how to test the sensor or get a replacenment for it.

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Cheers @frankjoke
Have amended title - forgot about the error history. :frowning:

In regard to all the other mentions - have done them all in trying to avert errors.

The funny thing about this situation was was that I had previously printed from the CFS without errors. So now sitting idle.
Then I printed from external spool, no problems.
Changed spool to send a different print.
Funny thing is I always do an extrude and retract before final extrude on external spool.

May be the extrude/retract buttons send some form of confusing signal ?