A guarantee/warranty is a bonus and cannot affect or diminish your statutory rights with the seller. A guarantee/warranty is a written statement given by a manufacturer or a company indicating they will repair or replace a product within a specified time after it was purchased. You may decide to claim under a guarantee during its period of validity, but cannot be obliged to do so.
Therefore you may, if the reasonable lifetime of a given product exceeds the time period of any warranty, pursue the seller in respect of your statutory rights - 'The Sale of Goods and Supply of Services Act, 1980'. If the trader refuses to offer redress for the faulty goods and you have exhausted all other options you may wish to pursue the matter with the Small Claims Court.
A guarantee may be useful to a third party, however, as it extends to anyone possessing the goods during the guarantee period. This contrasts with the statutory rights of a purchaser, which extend only to the original purchaser of a good and not to any subsequent recipient or owner of that product. This distinction in important to note in respect of items given as gifts or the purchase/use of second hand items.