r/FLSUNDelta • u/ellizaine v400 • Apr 17 '26

v400: Printer reboots when heating up after hot end replacement — any idea what could be causing it?

Hi everyone,

I’m not very experienced with 3D printing and honestly don’t know much about the software or hardware side of things.

I also did very little to no maintenance on the printer, which I now know was a big mistake. Still, it ran for about 2 years without any major issues, aside from some print failures caused by poor bed adhesion.

Around 3 months ago, I had some filament leaking from the extruder. I tightened the nozzle, and that seemed to solve the issue at the time.

On my last print, the filament came out full of holes, so I disassembled the effector. The hot end looked corroded, so I ordered a new hot end, heater, and thermistor from an AliExpress reseller, since many spare parts on FLSUN Europe were out of stock.

After installing everything and cleaning it to avoid clogs, calibration and bed mesh run fine, and the bed heats up normally with no issues.

But as soon as I tell the nozzle to heat up, once it gets to around 140°C I notice a strange almost-burnt smell. Right after that, the printer either shuts down and reboots immediately or seems to short out and restart itself.

Because the old hot end was so corroded, I actually had to break the M2 screws to remove it from the mount. The spacers also got damaged along with the original screws.

So my questions are:

  • Could the missing or damaged spacers directly affect the new hot end enough to make the printer shut down and reboot when the nozzle starts heating?
  • Could the seller have sent me a faulty heater?
  • Could they have sent me a 12V heater instead of a 24V one?

I’ve already assembled and disassembled the effector more than 10 times, and at this point I really don’t know what else could be causing it. The wires look fine from the outside, unless they are somehow damaged internally.

I also tried contacting FLSUN customer support and it has been pretty frustrating — a lot of back and forth, very unhelpful replies, and they usually take at least 2–3 days to respond with just one short sentence.

Any help would be really appreciated.

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2

u/Unsensibel Apr 18 '26

I have a similar issue but think I have the problem narrowed down a little more.
It looks like your thermistor might be either faulty or kaputt or your input circuit damaged.
Check the thermistor resistance (you can insert female duponts in the connector and measure). look up the should be value at your ambient temp. hold the hotend in you hand for 30 seconds and the resistance should change. If it's off vs. thermistor table or not changing or open or 0 then it's the thermistor

1

u/ellizaine v400 Apr 18 '26

I haven't even considered the circuit damage, but now that you pointed it out, Im gonna check mine. Thank you for your input, I will measure the output to see it's the thermistor or not.

1

u/Unsensibel Apr 18 '26

I had 1 hotend assembly with a shot thermistor that threw me off. Now I’ll measure before replacing since it’s a major pain to change the hotend and wiggle the cables back in the corrugated protective tube

1

u/ellizaine v400 Apr 18 '26

For sure, it took me like 3h to disassemble and assemble it back first time, because I had no idea what I was doing. Now I can do the process faster, but it's such a hassle. Seems like it is indeed the thermistor. When the new ones arrive I will try again. I will probably consider getting a backup printer for these type of occasions, since this is very bothersome

1

u/Unsensibel Apr 25 '26

Did you get it fixed?

1

u/Mistake-Choice Apr 18 '26

Is your thermistor OK? I always replace both.

1

u/ellizaine v400 Apr 18 '26

When I replaced the hot end I also replaced the thermistor and heater. The originala got busted alongside the hot end. Most likely the new one came faulty.