Washer-dryer takes excessively long to heat water; may show E12 during wash cycle

Safety first: Unplug the appliance and allow it to cool before inspection.

• 1. Descale the machine: Run a maintenance cycle with a Bosch-approved descaler or citric-acid-based cleaner at high temperature to remove limescale from the tub and heater.
• 2. Check heater performance: Access the heater as in E05 and inspect for heavy scale deposits. A heavily scaled heater should be replaced, as it heats inefficiently and can overheat locally.
• 3. Test heater resistance: Use a multimeter to confirm the heater is within specification. A significantly higher resistance than normal can indicate deterioration.
• 4. Verify NTC readings: If the NTC sensor is reading incorrectly, the control may think water is cooler than it is, extending heating time. Replace the NTC if readings are out of range.
• 5. If E12 persists: Have a technician check supply voltage and control board regulation.