Page summary triggering

I'd like to change <h1> html tag for page summary. Does it exist an option in system.yaml?

The page summary is rendered in an h1 tag? This part is controlled by the theme, not by Grav itself. Which theme are you using?

You need to detect which twig template renders that summary, and change the HTML code that wraps it.

I use a theme created by myself. The {{ page.summary }} in .twig file is rendered as "<h1>my summary</h1>". I don't be able to find where is this"<h1>" in my theme.

really need to see:

a) your page content .md file
b) your twig that renders the page

Perhaps you can put together a GIST with these files?

I found the problem in .md file: I forgot to "put this [summary separator] in your content with blank lines above and below". Sorry!

No problem, glad you got it sorted :)