If the remaining filament is uncertain, plan the change before the print starts. A runout sensor is useful only when it is enabled, working and supported for the loaded material.
Prusa’s IR-sensor documentation describes a model-specific pause and prompted change process. Use your own printer’s sequence; a presence sensor is not a universal clog detector.
Set up the replacement
- Choose a compatible filament formulation and diameter.
- Prepare it according to its storage and drying requirements.
- Check the spool’s feed route and retain its loose end.
- Confirm how the printer pauses, unloads, loads and resumes.
- Allow for a visible color or batch transition if appearance matters.
I do not trust the runout sensor
Use the manufacturer’s test procedure before the important job. If it fails, resolve the fault or start with enough filament. Do not rely on a sensor that has already missed a change.
Can I swap to another polymer mid-print?
Do not assume adhesion, temperature or profile compatibility. For an ordinary replenishment, stay with a compatible material. A deliberate multimaterial construction needs its own validated workflow.
Example: a normal MK3S/+ runout change
In Prusa’s IR-sensor workflow, enabled runout detection pauses printing and parks the carriage before prompting a change. This is the normal successful path, not a jam-removal procedure.
- Let the printer pause and park; use its unload prompt to remove the short remaining filament.
- Replace the spool with the same material type, prepare its tip and insert it when prompted, then press the knob to load.
- Inspect the extrusion at the confirmation prompt. If loading failed, choose the filament-not-loaded option; if the old color remains, choose the color-not-clear option for further purging.
- Confirm a successful change only when material is coming through correctly. Clear purge waste as instructed and allow the printer to resume.
If the remainder does not unload, stop this normal path and follow the model’s jam procedure. Prompt wording can differ by firmware; the source groups several MK3-family machines, so match your installed version. This IR presence sensor does not detect a clogged nozzle.
After the change
Follow the printer’s prompts, clear purge waste as instructed and inspect resumed extrusion. Do not manually move axes or pull on the part during a paused job. If surface continuity matters, use a planned change location rather than hoping runout occurs in a hidden area.
The remaining-filament guide can help decide whether changing before the job is simpler.
