It depends on the exact environment. If the blog posts and the pages are different custom post types, then choosing the correct post types will most likely do the trick. You can choose the post types under the General Options -> Sources panel, try choosing the ‘post’ only.
I think that now is alright 🙂 Is it better to find results in the title or in the text content? Now I only have the title option… What’s your recommendation? 🙂
It is definitely not the custom field, if you have the title selected for search under the General Options -> Sources panel. It is more likely an exclusion/inclusion. If you have any exclusions set, check if the item is not within the excluded date range, post tag, category, user etc..