Can one use LED flashlight (no filament) for bedikas chometz? Is it considered a ner?
Yes, this is fine.
There is no halachah of fire for bedikat chametz, but rather a halachah of light (the Gemara writes that the light of a candle is good to check with, and the light of a flashlight is usually even better). If the flashlight provides good light, there’s no reason not to use it, even if it does not have the halachic status of fire.