I am running Magento 2.2.3, apache 2.4, and have it set in the settings to use the built-in cache system. Varnish is not installed.
Full page cache is activated. There are no blocks which are set to not cacheable.
When I check the site headers i get:
Pragma no cache
Cache-Control max-age=0, must-revalidate, no-cache, no-store
additionally, when I go to the settings and switch from built-in to Varnish (despite varnish not existing on the server), i get correct cache-control headers.
any ideas on what could be causing this issue?
I don't believe that the full page cache will work if you are not using Varnish.
The built-in cache system is just the file cached that are located in /var/caches. If you see cache files populated under the directory, it means that cache is working.