A1s have a defect that can cause them to catch fire. Yours may be experiencing that? I'd be careful.
this post was submitted on 06 Jun 2026
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AFAIK it's a thermistor that is breaking causing thermal runaway. But this is can only happen during printing where heated/hotend is heating.
What you are thinking of is the NTC thermistor that was failing. That part was meant to limit the inrush current when the nozzle was rapidly heating. Its failure will just stop the nozzle from working at all. Which is precisely what should happen at failure. It is suspected they either got a bad batch of NTC thermistors or they were pushing the inrush current too close to the max rating. Bambu replaced a fair number of control boards and took the hit for not addressing these failures by not recalling the affected batch and replacing the offending board.
The plastic housing of the printer is a fire-retardant, high-temp polymer. And as far as I have read and know from my following of the issue, there have been no reported and verified fires caused by this particular problem. Just some scorched plastic and a bit of localized melting with the blown NTC.
But there does remain a non-zero chance of a real fire because of bad NTC. But it needs to be ignited by dust or little bits of filament that invades every nook and cranny on every printer in existence. If it bothers you and you are worried, clean your A1's insides every year. Make it a routine maintenance thing.
Disclaimer: I do own an A1 mini (which is not affected by this issue). While my mini does exactly what I originally bought it for (before the ongoing attempt of Bambu to crash the plane), I'm under no illusion that Bambu is not a company I wish to support.
I though we fixed thermal runaway firmware issues like a decade ago for good...
Not when the sensor fails so the feedback to the firmware controlling it is incorrect and there is no thermal fuse.
Yes, even when the sensor fails.
If the feedback from the thermistor is either nonsense or doesn't change as expected even when the heater is on/off for a certain time, that should trigger a thermal runaway error and halt the printer. That's basic decade plus old Marlin code.
I've had two broken thermistors in my Ender 3. First one reported negative temperatures when it disconnected, so the printer immediately halted with a min temp error. The second reported something like 150C, which was in the acceptable range, except when it tried to heat it up and nothing changed for like 15 seconds, which triggered a halt.
Again, decade old marlin code. Not rocket surgery.
Thanks! I have a Mini so haven't paid that much attention.
This issue does not affect the mini. That's a different control board. I own a mini.
What's the defect? Can you send an article or something? Is there a recall or something I should do? In what way do I "be careful"?
Make sure your printer is not on something flammable, have a smoke detector (are common practises for safety). Since the problem is about power draw, and heated bed is what needs the most i got a cool build plate so i'm now printing at 30°c instead or 60°c. Obviously, some could also replace the cheap component bambou has put in but i'm not confident enough with my electric skills.
About the issue, i recall that quite a few A1 got on fire. Bambu denied there was an issue and said it was a user fault. Some guys pointed out a weak component that would just barely support the maximum load printer can use and ranked it as unsafe. No recalls as no issues for Bambu
Is there any documentation about the fires? How did you find out about them?
As I know from reading various outside sources and have heard, there have been NO actual fires reported and verified caused by the NTC failure in question. Just some scorch marks and a bit of localized melting.
This does not mean that a fire is impossible, but that you would need to have an exceptionally bad day for the fire resistant plastic of the housing and board to catch fire.
Make sure your printer is not on something flammable
I'm currently building an enclosure for mine that is double layered with backer board (concrete) and drywall (high inflammability).
also adding in a smoke detector that can cut off the power with a backup thermistor that when triggered will cut off the power and set off an even louder alarm.
my hope is to have it sealed air tight enough that even if a fire were to start, it would quickly run out of oxygen to burn. I may lose the printer, but hopefully I won't lose my house.
my preference would have been to keep my printing to an exterior building but that's not possible right now.
I share this in hopes someone might get some inspiration and protect themselves from the inevitable fire that starts from the hobby.
See ExcessShiv. Looks like I'm wrong about it being possible while not printing.
What is the power threshold? Maybe it was just barely below it before, and a new something that runs at startup adds that extra couple of watts in CPU power triggering it.
If it spikes in the heating range during reboot maybe they added a new diagnostic check that briefly turns on the heaters?
Your first theory was mine as well. Although the power strip doesn't specify what the threshold is; I can set it to low/med/high. It's set to low.
For your second idea, I'll test it, but I believe it stays on indefinitely, not just for a few minutes after boot up
Unless the meassurement in your strip is wrong, I’d guess like you two that something in the FW makes it draw slightly more at idle.
An easy way to test this is to revert to an older FW. Can be done easily in Handy.
If that fixes it, you know it’s the printer. If not, then it’s probably the sensor in your strip.
Good luck!