Filament not melting in nozzle

Hello! I’d be grateful for any help anyone can offer with my printer problem. The forum instructions say to give lots of detail, so here’s the saga:

Filament isn’t coming out of either of my 0.4 nozzles (hardened or stainless). My 0.2 and 0.6 nozzles print fine, so I’m guessing it’s not an extruder issue. (I checked the extruder for broken filament anyway, and found nothing; I also tried extruding just the filament without a nozzle installed—both PLA and eSun 3d printer cleaning filament—and they went through fine.)

When I attempt to load filament into my 0.4 nozzles, the filament goes in a bit but then stops, extruder clicking. One of them had some black on the filament when I did a cold pull, but even after it was coming out clean, filament wouldn’t go through the nozzle (PLA or cleaning filament). The ends of the cold-pulled bits look to me like they weren’t actually melting (see picture)


even though the nozzle was reading as hot, and moving my hand close confirmed it was putting off heat.

My stainless 0.4 nozzle was working great for me over the past six months I’ve had the machine. Then one night, during a several-hour print, the filament stopped coming out. The machine kept trying to print even though there was no filament coming out—no error message—and boy was that filament jammed in tight. After I cut it and took the hotend out, it took a fair bit of yanking to get the filament out of it, even though the nozzle was around 220 degrees when I removed the hotend to pull the filament manually.

When the stainless 0.4 started refusing to extrude I’d thought maybe that hotend was going, so I switched to the hardened 0.4 , but it behaved normally for only a few days of printing before ceasing to extrude.

All nozzles are from the Bambu store, bought new, and I haven’t made any modifications to the printer or its parts. Aside from the eSun cleaning filament, which I tried today, I’ve only ever used PLA.

Regards.

The nozzles probably aren’t flowing because they’re plugged up. The amount of black stuff you get on the cold pull is unusual IMO. Looks like the extruder got way too hot and plastic burned in the hot end. A cold pull by itself may not be enough, which is why you also got a poker-needle thing with the printer. Be careful not to burn yourself, but heat the nozzle up and run that needle in to the extruder nozzle and work it in/out a few times. Then see if the nozzle will flow.

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Thank you so much! You were right, it was a nozzle clog. I followed your instructions, and after the nozzles spat a few large drops they started flowing. (I’d thought the nozzle-end of the filament from a cold pull was supposed to be more tapered, which was why I’d thought the problem was that the filament wasn’t melting in. I feel silly.)

If the problem was caused by the extruder overheating, do you have an idea why it might be doing so?