My DeLonghi automatic coffee machine insists on being descaled at regular intervals, despite the fact that I use rain water and no scale can form. It does so by illuminating an indicator light hidden below the grind adjustment knob:

In addition, the instructions are so appallingly bad that it takes me 15 minutes to fight my way through them even before I can start. Here's what needs to be done:

1. Turn machine off, remove grounds.
2. Fill water container with 100 ml descaler and fill to the top with water. I use just water.
3. Place a 1.8 litre container (not supplied) under the output spout and cappucino spout. Turn on and allow to perform normal startup.
4. Press the red button under the main knob for about 5 seconds. The LED will go on if it isn't already (though you can't see it, since it's under your thumb), and the others will go out. The LED next to the inverted mushroom cloud at top right will light.
5. Turn on the steam tap at top left (270°, marked 1). The mushroom cloud LED will go out and the device will start the descaling process.
6. After about 25 minutes, the liquid will have been processed. The “water out” and mushroom cloud light. Turn tap to mark 0 (0°), drain container, rinse the water container and fill again. Replace, turn tap to 1.
7. After a few minutes, the flush is complete. Repeat exactly: Turn tap to mark 0 (0°), drain container, rinse the water container and fill again. Replace, turn tap to 1.
8. After a few minutes, the flush is complete, and the red LED goes out. Turn tap to 0. Done!