When water boils at 100 °C, it evaporates as pure gas and leaves its dissolved minerals (calcium and magnesium carbonates) at the bottom of the heating chamber:
- Loss of thermal efficiency: Under repeated heat exposure, minerals precipitate and form a compact layer of calcite. This thermal insulator slows heat transfer from the aluminium to the water, increasing heat-up time.
- Wet steam and spitting: Without sufficient heat energy, the steam loses thermal energy and immediately condenses into liquid water droplets inside the hose.
- Thermal safety devices tripping: Insulated by the limescale layer, the heating element overheats, causing the thermal safety fuses to cut out prematurely.