Page Options: Check this box to hide the title

Page Options:
Check this box to hide the title

I use that option on all pages.
However… this option, does NOT remove the title in the source code.
All it does. It’s hiding it.

I need to REMOVE the title from the source code as well, otherwise I am running into SEO issues, having multiple H1 Tags on each page.

Question:

What’s the name of the .php file?
What’s the line of the code that needs to be removed?

nothing?

It must be possible to remove the actual source code.
Does nobody know what line of the code it is?
And in which file I have to remove it?

appreciate it any little help!