Display shows F3 and the machine does not heat water or steam properly.

Safety first: Unplug the machine. Heating components operate at mains voltage and can cause electric shock.

User-level checks:

• Reset and cool down: Allow the machine to cool fully, then reconnect and test. Sometimes an overheat protection can reset after cooling.
• Descale: Heavy limescale on the thermoblock can cause overheating and heater faults. If the machine will run a descaling program, perform a full descale with Melitta descaler.

Advanced checks:

• Remove covers to access the thermoblock or boiler.
• Inspect heater terminals and wiring for burning, loose spades, or melted insulation.
• Use a multimeter (with power disconnected) to check continuity of the heating element and thermal fuse. An open circuit indicates a failed component.
• Inspect the control board for a burnt heater relay or tracks.

Replace the thermoblock/heater assembly or thermal fuse as needed. If the heater and fuse are good, the control board is likely defective and should be replaced by a qualified technician.