E04 appears and the machine stops brewing; sometimes accompanied by water leaking into the drip tray instead of the cup.

Safety first: Unplug the coffee maker and allow pressure to dissipate for at least 15 minutes before opening any part of the hydraulic circuit.

• Remove and clean portafilter or filter holder: For pump espresso models, remove the portafilter and thoroughly clean the filter basket holes with a pin or brush. For capsule models, remove the capsule holder and rinse under hot water.
• Clean coffee spouts: Use a fine needle or cleaning brush to clear any dried coffee from the spout outlets. Run a hot water cycle without coffee to flush.
• Adjust grind: If using an external grinder, set it to a coarser grind and avoid tamping too hard. Overly fine coffee can cause E04 by blocking flow.
• Descale the machine: Run a full descaling cycle to clear internal scale that can restrict flow and raise pressure.
• If E04 continues: The internal overpressure valve or hydraulic block may be stuck or faulty. This requires disassembly and should be handled by an authorized Ariete service center.