How to set up syntastic for vim?

Try adding this to your vimrc:

let g:syntastic_check_on_open=1
let g:syntastic_enable_signs=1

(This is lifted straight from my vimrc, which has some other Syntastic settings if you'd like.)

I don't really understand the reason, but when I re-installed the YouCompleteMe plugin for vim with ./install.sh --clang-completer. Syntastic works like charm.