Firmware & Slicer Software

The Ender 3 runs Marlin firmware, either Creality's stock build or a community/custom build. Because of the thermal runaway protection gap covered in Error Codes & Safety, flashing a properly configured Marlin build is one of the most worthwhile things you can do with this printer.

Choosing a firmware build

Stock Creality firmware — works, but on many units ships with thermal runaway protection disabled for the bed. Check your version's release notes before trusting it as-is.
Community Marlin builds (compiled for your exact board revision) — typically ship with thermal protection properly enabled for both hotend and bed, plus often add linear advance and better default acceleration.
Always match the firmware build to your exact mainboard version (printed on the board itself) — flashing the wrong board's firmware can brick the controller.

Warning: Back up your current EEPROM settings (or note down your bed leveling values) before flashing new firmware — a fresh flash usually resets these to firmware defaults.

Flashing process (high level)

Download a build matched to your board (8-bit boards use .bin files copied to a microSD card; some newer boards support flashing over USB).
Insert the microSD card with only the firmware file on it and power on the printer — the screen will flicker while it flashes, then reboot to the standard interface.
Immediately re-level the bed and re-set your Z-offset — a firmware update always requires this.

Slicer setup

Ultimaker Cura and PrusaSlicer both have official or community-made Ender 3 profiles — search for your exact model in the built-in printer list rather than manually entering build volume and settings.

Set build volume to 220x220x250mm for the standard Ender 3, or 220x220x265mm for the V2 (confirm against your specific unit).
Start with a 0.2mm layer height and 200-215°C nozzle / 50-60°C bed for PLA as a baseline — see Slicer Settings Explained for what each setting actually changes.
If you've upgraded to a direct-drive extruder, reduce retraction distance significantly from Bowden defaults (typically 1-2mm vs 5-6mm) — using Bowden retraction settings on a direct-drive setup causes gear grinding.