An electric kettle usually stops working for a small number of repeat reasons: power connection failure, thermostat malfunction, dry-boil protection activation, scale buildup around the heating system, or internal component damage after long service. International kettle safety rules for appliances that heat liquids are covered by IEC 60335-2-15, which is one reason reliable manufacturers put so much attention on thermostat response, temperature limiting, and cut-off stability during development and inspection.