Can't change default product order

I am trying to change the default sort order of products to price in Version 2.1.0.2. I have edited catalog/controller/product/category.php to the following but it hasn't made any difference

if (isset($this->request->get['sort'])) {
$sort = $this->request->get['sort'];
} else {
$sort = 'p.price';
}

I have since changed some of the code so that the php would be invalid but the page is continuing to work exactly the same. I have cleared the cache within opencart and my browser caches and also physically cleared out the files within system/storage/cache but the error still isn't being reflected so I can only assume something is overriding this file although if I rename category.php to bak-category.php then none of the products appear as you would expect.

I'm pulling my hair out over this and I'm bald already!! so any help would be greatly appreciated.