A1 and A1 mini: Z homing or bed levelling fails (hotend eddy current sensor)
Guide based on the manufacturer's official documentation; usi3d has not yet verified it on a machine.
Technology: FDM · Brand: Bambu Lab · Symptoms: Homing or a sensor fails (endstop, levelling), Unlevel or warped bed, The printer shows an error code or message · Updated on 9 October 2026
Symptom
The A1 or A1 mini reports «Z homing failed» or levelling fails: the toolhead comes down a little and stops without touching the bed, drops quickly and goes back up, taps the same spot many times or «touches» in mid-air. Alerts such as 0300-1800-0001-0001 (hotend not detected), 0300-1800-0001-0002 (low sensitivity), 0300-1800-0001-0004 (abnormal sensor data) or 0300-1800-0001-0005 (Z motor stuck) may appear.
Likely causes, from most to least likely
- The eddy current sensor above the hotend, which detects when the nozzle touches the bed, gives no data: loose wire on the toolhead (TH) board, sensor damaged by rough hotend fitting or a blob on the nozzle, or a faulty TH board.
- Hotend not fitted, badly seated, with its top fin bent downwards, or a third-party hotend.
- Something is holding the Z axis back: a part left on the plate, debris on the lead screw rails or a bent lead screw.
- Inconsistent touches: vibration around the printer, a dirty nozzle or a loose hotend.
- Mid-air touches: old firmware, or sharply bent PTFE tubes pushing on the toolhead hub.
- During levelling: filament stuck to the nozzle, a loose bed or a soft spot, or lost steps on X or Y.
Checks to tell which one it is
- Watch how it fails: if it comes down a little and stops, suspect the sensor; if it drops fast and rises again, the Z axis; if it taps the same spot many times, the nozzle or stability.
- For Z homing the nozzle must be at 140 °C or below: above that, it homes X and Y first and waits for it to cool.
- With the nozzle cold, try to move the hotend by hand: it should not wobble.
- Remove the hotend and check whether the top fin is bent downwards (it should be flat or slightly upwards) and whether the sensor on the extruder is damaged.
Before you start
Before taking anything apart, cleaning or adjusting it, switch the printer off and unplug it, unless a step says otherwise, and do not touch the nozzle, the heater block or the bed until they have cooled down. If in any doubt about electricity, heat or moving parts, stop and ask a professional.
Step-by-step fix
Check the hotend
With the printer off and cold, remove the hotend, check the top fin and refit it properly. Use the official hotend: third-party ones can cause this error. Then press the homing button on the screen.
Check: Homing completes.
If that does not fix it: Check the sensor (next step).
Check the sensor and its wire
With the printer off, check that the sensor wire is held firmly by its screw on the TH board; tighten it if loose. If you have a multimeter, check continuity. Do not remove the black acetate tape from the sensor: its coil can break.
Check: The sensor alert disappears and homing completes.
If that does not fix it: If the screw on the board is broken or the sensor is damaged, contact Bambu Lab support.
If the Z motor gets stuck
Remove any part left on the plate, clean the debris off the Z lead screw rails, lubricate them and try again.
Check: The toolhead comes down and touches the bed without dragging.
If that does not fix it: If a lead screw is bent, record a video and contact Bambu Lab support.
If it taps the same spot repeatedly or touches mid-air
Put the printer somewhere stable, clean the nozzle and tighten the heater assembly screws. Update the firmware and tidy the PTFE tubes at the toolhead hub so they do not push on it and have nothing hanging from them. If it continues, loosen the heater assembly screws, press it down and retighten them, or replace the hotend.
Check: Homing finishes at the first attempt.
If that does not fix it: Contact Bambu Lab support.
If levelling fails
Clean the nozzle if filament sticks to it, check that the bed is not loose (tighten its screws) and inspect the Y axis rails. If the toolhead loses steps and touches the silicone wiper or moves off the bed while levelling, look for obstacles on X and Y.
Check: Levelling finishes without repeated touches.
If that does not fix it: Record a video of homing and levelling and contact Bambu Lab support.
Full levelling after changes
After changing the bed, the plate, the hotend or the heater assembly, run auto bed levelling from the Calibration page: it measures far more points than the levelling before a print.
Check: The first layer is even across the whole plate.
If that does not fix it: Check how the hotend is held using the A1 series first layer guide.
Prevention
- Stand the printer on a flat surface with all four corners supported.
- Fit the hotend carefully and always use the official one.
- Keep bed levelling enabled before printing, especially after changing the plate.
Still not fixed?
Tell usi3d's AI about your case: choose your printer, describe what you see and add photos if you like. It proposes checks step by step, with their sources.
Printers it applies to
The Bambu Lab A1 family: A1 and A1 mini.
Official sources
This guide summarises the official documentation linked here:
This guide is general information: usi3d has summarised it from the official documentation linked here, and it may not match your model, its version or its firmware. If in doubt, follow the manual and the support of your printer's manufacturer. You decide what you do with your machine, and working on it may affect its warranty.