DIAGNOSIS The machine has reached its programmed internal descaling timer. The orange descaling light is a mandatory service indicator, not a suggestion.
FIX You must complete a descale cycle. Prepare a container that can hold at least 1 liter. Fill the water tank with fresh water and Nespresso descaling solution (or 100ml of white vinegar). Place the container under the coffee outlet and the milk frother. Turn the machine off. Press and hold the Lungo button for at least 5 seconds until all three lights flash. Release. The machine will begin pumping the solution. Follow the prompts to rinse the system twice with clean water. The light will turn off.
IF THAT DIDN'T WORK If the light persists after a correct cycle, the internal counter may not have reset. Unplug the machine from the wall for 5 full minutes. Plug it back in and try the descaling procedure again from the start.
HEADS UP Do not use citric acid-based descalers. They can damage the thermoblock. Only use Nespresso's solution or plain white vinegar.