Hotend fan always runs

Recently, after last update I presume, the hotend fan (not the Part cooling fan, but the one on the side of the hotend, blowing on the heatsink) has been running non-stop at all times, no matter what, even if the hotend has cooled down to ambient temps, around 23-25C.

It even runs at 100% after restarting the printer, and it sitting idle.
I’ve tried letting it run overnight, but it still runs at 100% after sitting idle for 10+ hours.

This didn’t happen before, and the fan would shut off shortly after the hotend would reach 30-ish degrees.

Firmware version(s):

I have also tried to factory reset the machine, changing hotend assembly including the fan, but the issue still stands.

I’ve seen posts about the LED not turning off automatically, and the MC Board fan not turning off automatically, but not any posts about the Hotend fan not turning off.

Anyone have same issue?
Any help would be appreciated.

Thanks in advance.

If you turn off the power and restart does the fan come immediately back on or does it wait, and if it does wait, when in the power on cycle does it turn itself on again?

Thanks for your reply.

It turns on as soon as the Aux fan turns on in the boot cycle. The Aux fan turns off immediately afterwards, but the hotend fan stays on.

So about 0.5 seconds after turning the printer on.

I have now also tried using

M106 P0 S0
M106 P0 S0
M106 P0 S0
M106 P0 S0
M106 P0 S0

M107 P0
M107 P0
M107 P0
M107 P0
M107 P0

in the Machine end G-Code, but to no avail unforunately.

Did you find a fix for this? I am having the same issue.

Hello Sincidius,

I basically tried everything, and nothing seemed to work. I couldn’t test G-Codes by sending G-Codes directly to the printer, so individual testing of each fan would be too time consuming for me.

Therefore, I turned to Bambu Support, and they sent out a replacement shortly after getting in touch, and I received it a few days later.
The replacements they sent, were the Toolhead cable from the main board to the toolhead board, a replacement of the Toolhead Board, a replacement of the Toolhead Board FPC Cable, and lastly a replacement of the Extruder Connection Board.
I replaced the Toolhead Main Board and the Toolhead Board FPC Cable, and the fan began functioning properly after the swap. I am convinced it was the Toolhead Main Board which was the issue, since it had some minor blemishes on it, which I unfortunately only noticed after replacing the board, and I didn’t take any pictures of it.

If you have already tried to re-seat the cables, to make sure the connections are proper, I can highly recommend getting in contact with Support, and explaining your issue.

Hopefully you will get your issue solved swiftly.

Best regards.

Thanks! I actually ordered the parts this morning. I troubleshot down to the board or cable and think I powered it up when something was off. Since I figured it was my fault I just got the parts.