HMS 1A00-0100-0002-0021: No Hotend Detected on the Toolhead While Nesting
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HMS 1A00-0100-0002-0021 means the machine started to nest a hotend into the rack and found nothing mounted on the toolhead to nest. Bambu asks you to mount the hotend onto the toolhead before continuing, which is the fix in most cases: the sequence expects a tool in hand.
Note which end is empty. This is the toolhead, not the slot, and that distinction decides where you look.
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Mount it, then continue
If the toolhead genuinely has no hotend, fit one and click through. That happens after a manual intervention, after a cancelled job, or after a power interruption left the machine mid-sequence with the tool back in the rack rather than on the carriage.
Mounted, but not detected
A hotend fitted and still reported missing is a detection problem rather than a handling one. Debris in the mounting area holds the hotend a fraction proud, and that fraction is enough. Power down, look into the mounting slot on the toolhead, and clear anything you find before reseating.
When the sensor is the answer
If a hotend you can see and feel is still invisible to the machine after a clean reseat, the presence detection is at fault, and that has its own message: HMS 1A00-3000-0001-0040 names the sensor as open-circuit. Reseating the toolhead connector is the first thing to try there.
How HMS 1A00-0100-0002-0021 differs from the empty-slot code
An empty rack slot is HMS 1A00-0100-0002-0003. This code is the opposite end of the same move: the destination is ready and the source is empty. Reading which one you have saves opening the wrong half of the machine.
Handling hotends without causing the next fault
Hold them by the body rather than across the mounting faces, and keep them off the bench surface where they pick up dust. Clean faces are what the detection and the grip both depend on — the hardware itself is described in 3D printing hotends, and the platform in the Bambu Lab H2D.
HMS 1A00-0100-0002-0021 FAQ
Can I continue without mounting one?
No. The operation is putting a tool away, so it needs a tool to put away.
Why did the toolhead end up empty?
Usually a cancelled job or a manual swap. A power cut mid-sequence does it too.
Does it matter which hotend I fit?
For clearing the message, no. For the print, fit the one the plate expects.
Could the lock be at fault?
If the hotend will not seat at all, check the locking lever — see HMS 1A00-0100-0002-0024.
Sometimes the machine cannot confirm either end. HMS 1A00-0100-0002-0022 names both preconditions at once, which means you are recovering a state rather than fixing one thing.
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