That crest is very characteristic of a goldcrest. I know of two sub species of gold crests, one has the yellow stripe the other a slightly orange stripe and body
This seems to me like the goldfinch, regulus regulus. Not the common firecrest , regulus ignicapilla.
My information sources is the Merlin Bird spotting app.
EDIT: the correct name is not goldfinch but goldcrest. As it is not in the finch family at all.
I probably should have said where i am located, it's in Düsseldorf, Germany. Regulus regulus should be around where i live too, according to my local bird book, but i have not seen one yet, i am quite certain it must be the child of Carduelis carduelis, European Goldfinch, the older ones are all over the feeder: