This obviously depends on a lot of factors including build quality and your local conditions. In general, however, most products offer a warranty of 10,000-20,000 working hours. For reference, a year has 8760 hours, but you won't really expect your pump to work throughout the night as well, so the warranty should realistically cover 2-4 years. This doesn't mean it will go bad the first hour after the warranty runs out (Murphy's law isn't always right). In practice, you can expect the pump to run for a few years. But don't skim on basic maintenance -- changing a filter or cleaning the solar panel once a year can make a good difference.