HMS 1A00-0100-0002-0003: Hotend Swap Check Failed, No Hotend Detected at Slot
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HMS 1A00-0100-0002-0003 means the machine ran its pre-swap check, expected to find a hotend sitting in that rack slot, and detected nothing there. Either the slot really is empty, or the hotend is present but seated badly enough that the detection does not register it.
The check runs before the swap rather than during it, which is the useful part: nothing has moved yet when you get this.
Where to buy
Look at the slot before anything else
The simplest explanation is the right one more often than people expect. A hotend removed for cleaning and not returned, or returned to a different slot than the print expects, produces exactly this message. Open the machine and count what is actually in the rack against what the plate asked for.
Seated, but not seated enough
A hotend pushed in until it feels home can still sit a millimetre proud if filament residue or a fragment of purge is under it. Detection works over a short distance, so a small gap reads as absence. Lift it out, clear the slot, and reseat it until it is flush rather than until it stops moving.
Then the detection itself
If a hotend you can see and touch still reports as missing in that slot, the fault has moved to the sensing. A wiring fault reports separately and more specifically — see HMS 1A00-3000-0001-0040, which names the presence detection sensor outright.
What HMS 1A00-0100-0002-0003 does not mean
It is not the opposite fault. When the machine finds a hotend where it expected an empty slot you get HMS 1A00-0100-0002-0004 instead. Reading which direction the mismatch runs tells you whether to add a hotend or remove one, and that is the whole decision.
Keeping a rack honest
A tool-changing printer only works if its idea of what is loaded matches reality, which means putting hotends back where they came from rather than wherever is free. Background on how this generation of machine is built is in the Bambu Lab H2D, and what hotends themselves actually do is in 3D printing hotends.
HMS 1A00-0100-0002-0003 FAQ
Can I carry on with fewer hotends?
Only if the sliced plate uses fewer. A file that calls for a tool the rack does not hold will stop here every time.
Does the slot number matter?
Yes. It tells you exactly which bay to open, which saves inspecting the whole rack.
Will reseating always clear it?
When the hotend is genuinely present, usually. If it survives a clean reseat, treat it as a sensor fault rather than a handling one.
Is this the same as a failed swap?
No. This is the check before the swap, which is why nothing is stuck when it appears. Mechanical failures mid-swap read differently — see HMS 1A00-0100-0002-0026.
The same check fails the other way round too. HMS 1A00-0100-0002-0021 means the toolhead was empty when the rack went to nest a hotend, which sends you to the carriage rather than to the bay.
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