Featured image transforms into header image

Hello, i hope i can get some help with my site: http://www.eduardolaveglia.com/ I have set up a heder image that replaces the original one (the one of the Budha that comes with the theme). I want that image to be on EVERY page and post of my site. The problem is that in my recent post i put a featured image and that image replaced my header for that post. Im previous posts i have seted a featured image and this didnt happen. I dont know why now is changing my header image. Please help and thenks in advance!