Clogged Nozzle and Hot End Jam: How to Fix Them

A clog or jam is one of the most common 3D printer problems. Here is how to spot it and fix it safely.

Signs of a clog

Thin or missing lines, under-extrusion, a clicking extruder, or filament that will not come out.

Clearing a clogged nozzle

• Heat the nozzle to the filament's printing temperature.
• Push the filament through by hand, gently.
• If it stays blocked, do a cold pull: with filament loaded, lower the temperature until the filament is soft but not runny, then pull it out firmly. Repeat until the tip comes out clean.
• If the clog will not clear, replace the nozzle.

Hot end jam

A jam higher up in the hot end often happens when heat travels too far up (heat creep), for example from a weak cooling fan. Check that the heat-sink fan runs, the nozzle and heat break are tight, and the temperature suits the filament. Then heat up and clear the filament as above.

Changing a nozzle

• Heat the hot end to printing temperature. Keep your hands away from hot parts and use tools.
• Hold the heater block steady with one wrench and unscrew the nozzle with another.
• Screw in the new nozzle, and tighten it snugly while hot. Do not over-tighten.
• Let it cool, then check the tightness again after the first heat-up.

This is general guidance. Always follow your printer manufacturer's instructions.

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