This issue might help someone out there that had the same problem as I did when upgrading a shop from an older version of Prestashop.
I upgraded from 1.3.x to 1.5.x using the manual upgrade whereby I copied all images across and migrated the database etc. When I performed the upgrade to 1.5 all looked well until I clicked on manufacturers and no products where showing. The message I kept getting was:
“No products for this manufacturer.”
From the back office all products were associated with the correct manufacturer so it seemed to be a front end issue.
After tearing my hair out and comparing the database tables with a sample prestashop install I started trying all sorts of settings at the back office. In the end it turned out to be a simple filter issue.
I went into preferences->products and scrolled down to the pagination section and changed the filter from manufacturers to product name and it worked a charm.
Essentially what seemed to be happening is when manufacturer was clicked the default pagination was set to manufacturer and this was causing a filter issue. Changing it to product name solved that issue and now the products display when manufacturer items are clicked.