DIAGNOSIS The orange light is the 'Descale' indicator. The machine has calculated it needs a cleaning cycle.
FIX You must run the built-in descale mode. Turn the machine off. Press and hold the 8oz and 12oz buttons together for 3 seconds. The 'Descale' light will blink. Run a full water reservoir of a 50/50 mix of white vinegar and water through the machine, followed by several reservoirs of clean water, until the orange light turns off.
IF THAT DIDN'T WORK If the light persists, the water sensor might be faulty. Ensure the reservoir is seated perfectly. Try a full factory reset: unplug the machine for 1 minute, then plug it back in.
HEADS UP Do not use citric acid-based descalers with this model. They can damage the internal thermal components. Only use the vinegar solution or Keurig's official descaling solution.