Only 20 posts being displayed on site

Hi guys,

I have had a wordpress theme developed for me, and the developer has since become unreachable. I just need to trouble-shoot a few things with it.

The home page displays all the posts, and they also get added to a sub-menu on other pages. The strange thing is that the site only seems to allow 20 posts to be displayed. I find that changing the published date is the only thing that allows a post to be prioritised and appear, but then obviously one drops off.

Is there a setting or something in wordpress that might control either the number of posts allowed, or whether a post that falls outside a certain published date will be hidden?

I’m not able to send a link to the dev version because it’s running securely. I can provide snippets of code though if that helps?

Any help is appreciated, it’s driving me insane.