A1 Hotend not heating up

[Calendris]

Hello,

my A1 with AMS doesn’t heat up my Hotend anymore.
Yesterday I switched from 0.4mm nozzle to 0.4 hardenend nozzle. (heated up, cutted the filament, and than exchanged the Hotend) after that my Hotend/Nozzle wont heat up anymore. it goes to 40°C and than nothing more happends (on manually heating).
i touched it and its cold.
If im going to do a print i get an error code

Which part do i need to replace? Hotend Heating Assembly - A1 Series or/and Toolhead Board - A1 Series?
Hope maybe you guys can help me

[BambuBanker]

When replacing did you do anything besides unclipping the old one and clipping in the new one?

[Calendris]

No i just unclipped the “old” one, put it on the heatbed and placed the new one and closed the clip.
After i recognized the problem i tried a few time switching to see if there is a problem, but everything looks fine and in place for me

[BambuBanker]

Is it possible there is a small piece of debris between the nozzle and heating element causing it to not heat up?

[Calendris]

Disassembled the “head” and a small piece fell out, its not even filament, just a black piece of Something now it works again.

Thanks!