Coffee Machine Descale Message Will Not Go Away

What it
usually means.

The machine does not see scale. It counts the water that has passed through it and, from the water hardness the owner set, estimates when scale will build up; then it asks for a descale. If a filter is registered, it counts the filter instead and asks less often. That counting explains most messages that will not clear. A cycle that was stopped halfway, whether the tank ran dry, the power went off or someone pulled the tray, does not count, and the message stays. Many models also insist on their own sequence: descaler in the tank, empty the tray at the step it asks, then rinse water, with the whole cycle run in one go. A hardness setting left at the factory level on soft water makes messages come too often; on very hard water with no filter, too rarely. A filter fitted without being registered in the menu, or left past its end, changes the count too. Only when a correct, uninterrupted cycle leaves the message in place is the board or a sensor worth a look.