CALC or descaling indicator LED stays on or flashes; the machine still brews but prompts for maintenance.

Safety first: Follow the descaling instructions carefully. Use only Senseo-approved or citric-acid based descaler. Never use vinegar unless explicitly allowed by the manufacturer.

• Prepare descaler: Mix descaling solution according to the product instructions and fill the water tank.
• Run descaling program: Start the descaling cycle (often by pressing both cup buttons simultaneously). Collect the hot solution in a large container.
• Pause and soak: If the manual suggests, pause halfway to let the solution sit in the boiler and lines for 10–15 minutes.
• Rinse thoroughly: After descaling, rinse the tank and run at least two full tanks of clean water through the machine to remove any residue.
• Reset indicator: On some models, hold a specific button combination (e.g., CALC button or both cup buttons) to clear the CALC light after descaling.