Bambu A1 and P1S clogged extruder: causes, diagnosis, and fix

Signs your extruder is clogged

The most obvious sign is under-extrusion: your print has gaps, weak layer adhesion, or thin walls where there should be solid fill. You may also hear a rhythmic clicking or grinding from the extruder motor — that is the drive gears skipping because they cannot push filament through a partial blockage.

Other signs to look for:

• Filament loads but nothing, or only a thin thread, emerges from the nozzle
• A print starts normally then progressively weakens over several layers
• The AMS or AMS Lite reports a runout when the spool is clearly not empty
• The printer pauses mid-print and cannot resume extrusion

On the P1S, the enclosed chamber keeps ambient temperatures higher than on the open-frame A1. This is normally a benefit for ABS and ASA printing, but it can accelerate partial clogs: heat creep may soften filament above the melt zone, forming a plug in the heat break during a long pause.

Why clogs happen on Bambu machines

Most clogs on the A1 and P1S fall into one of four categories.

1. Carbonised filament. Leaving the nozzle at printing temperature for more than 10–15 minutes without extruding causes the material to degrade and char inside the bore. A long AMS jam, a paused multi-colour print, or forgetting to unload before switching off are common triggers.

2. Moisture in the filament. Wet filament bubbles and snaps inside the hotend, leaving small fragments that accumulate into a blockage. PLA and nylon are especially susceptible; a spool left open in a damp room can absorb enough moisture overnight to cause problems.

3. Incompatible material changes. Switching from a high-temperature material such as ABS or ASA to a lower-temperature one like PLA without fully purging can leave residue that solidifies at the lower temperature and narrows the bore over successive prints.

4. Filament grinding. A partial clog makes the extruder work harder. Eventually the drive gears chew through the filament strand rather than advancing it, and the resulting dust compacts the blockage further.

The A1 and P1S share a very similar all-metal hotend design and default 0.4 mm brass nozzle. The diagnosis and fix steps below apply equally to both models.

Before you start

You will need:

• A spare length of the same filament type, or a reel of PETG or nylon (nylon is the classic choice for a cold pull)
• An acupuncture needle or commercial cleaning needle, 0.3–0.35 mm diameter
• Tweezers
• A silicone pad or folded cloth to catch molten filament drops

Disconnect the filament tube from the toolhead and turn off the AMS or AMS Lite before starting any manual work on the hotend. On the P1S, open the front door to give yourself clear access. Never touch the heater block or nozzle with bare fingers — both get well above 200 °C.

Step 1 — Try the built-in purge first

Before dismantling anything, use the machine's own routines.

1. On the printer screen, go to Filament > Unload filament and let the machine retract whatever is loaded. 2. Go to Filament > Load filament and push a fresh length through. 3. Watch the nozzle tip. If filament emerges cleanly, run two or three additional purge lines at your printing temperature plus 10 °C — for PLA that means 220–230 °C rather than 210 °C.

If filament loads but nothing comes from the nozzle, or only a thin trickle appears, move to the cold pull.

Step 2 — Cold pull (atomic pull)

A cold pull drags the softened plug out of the nozzle from above. It leaves no debris behind and is the safest method to try before anything more invasive.

The correct cool-down temperature depends on the material:

• PLA: heat to 230 °C, cool to 85–90 °C
• PETG: heat to 240 °C, cool to 60–65 °C
• ABS or ASA: heat to 250 °C, cool to 95–100 °C
• Nylon: heat to 250 °C, cool to 80–85 °C

If you are unsure what is causing the clog, nylon filament often works better than whatever material caused it.

1. Heat the nozzle to the upper temperature above and manually push a length of filament through until you see any extrusion at all, however thin. 2. Set the nozzle to the lower cool-down temperature and wait. Do not let it cool all the way to room temperature — you want the filament pliable but not liquid. 3. When the target temperature is reached, grip the filament firmly close to the toolhead entry and pull in one smooth, firm motion without jerking. 4. Inspect the pulled tip: if it is tapered cleanly and free of grey or black specks, the bore is clear. If it is blunt or discoloured, repeat from step 1.

Plan for three to five pulls on a badly carbonised nozzle. If there is no improvement after five attempts, move to needle clearing.

Step 3 — Needle clearing

This method is more aggressive. Pushing a needle through the nozzle risks compacting debris further up the heat break if done incorrectly; use it only if cold pulls make no progress.

1. Heat the nozzle to printing temperature plus 20 °C. 2. From below, through the nozzle tip, insert the cleaning needle with a gentle back-and-forth motion. Do not force it. The aim is to break up the carbonised mass, not to drive it upwards. 3. At the same time, apply light downward pressure on the filament from above to encourage freed debris to travel down and out through the tip rather than up into the heat break. 4. Withdraw the needle, then purge with fresh filament for 10–15 seconds and wipe the nozzle tip clean. 5. Follow up with a cold pull to remove any remaining loose fragments.

If the needle will not enter at all, the blockage is a hard carbon plug jammed at the very tip. At that point nozzle replacement is faster than persisting with clearing.

Step 4 — Replace the nozzle

The A1 and P1S both use standard Bambu-format nozzles that unscrew from the heater block. Genuine replacements are available from Bambu Lab directly; third-party versions are also widely available, though quality varies.

Note that opening the hotend assembly yourself will void whatever remains of your Bambu warranty. Check your purchase date before proceeding.

1. Heat the nozzle to 250 °C to soften any residual filament. 2. Unload the filament completely. 3. Using the spanner included in Bambu's maintenance kit (or a 7 mm open-ended spanner), unscrew the nozzle anti-clockwise while steadying the heater block with your other hand. Keep the block still — twisting it risks tearing the thermistor or heater cartridge wires. 4. Thread the replacement nozzle in while the block is still warm and tighten it snugly. Do not over-tighten — brass nozzles are soft and the threads strip easily. 5. Heat to 250 °C once installed and run a cold pull to clear the bore and seat the nozzle properly.

Preventing future clogs

• Never leave the hotend sitting at temperature for more than a few minutes with no filament moving through it.
• Dry wet or older filament before printing: a food dehydrator at 45–50 °C for four hours suits PLA; PETG and nylon benefit from 60–65 °C for six to eight hours.
• When changing from a high-temp to a low-temp material, purge at least 200–300 mm of the new filament through before starting a print.
• After printing with carbon-filled, glow-in-the-dark, or other abrasive filaments, run a cold pull at the end of the session.

When to mail it in

If cold pulls and needle clearing have not shifted the blockage — or if a cleaning needle has snapped inside the hotend — the repair becomes more involved. A jammed heat break can be seized solid and requires careful disassembly that risks tearing the thermistor wires. If the extruder motor has been skipping against a stubborn clog for some time, the drive gears may also need inspection or replacement. These are fiddly jobs with a real risk of making a fixable problem worse. Send it to us at harktech.co.uk/contact.html with a note of what you have already tried, and we will diagnose, clear the blockage or replace the necessary parts, and return it within a few working days.