The Sale of Goods Act says that any item sold in the UK must be of satisfactory quality, fit for purpose, and as described. If it isn’t or the item is faulty you are entitled to a repair, replacement or refund. New legislation is currently going through Parliament to specify exactly what a consumer is entitled to claim when a product that they buy is faulty.
Since June 2014, buyers of items purchased on-line, by telephone or mail order have 14 days from the date of delivery/installation to assess the product and decide if they want to keep it. This has nothing to do with whether a product is faulty and is merely to allow consumers to assess a product in their own home as well as they would if buying a product in a face to face sale in a shop.