Machine displays E03 and will not brew; sometimes accompanied by no water flow from spout.

Safety first: Unplug the machine before any disassembly. Hot water and steam under pressure can cause burns.

• Check water tank and filter: Ensure the tank is full and correctly seated. If a water filter cartridge is installed, remove it and test without the filter in case it is blocked.
• Run hot water cycles: If the machine allows hot water dispensing, run several cycles to see if flow improves. Intermittent flow suggests partial blockage.
• Descale thoroughly: Run the descaling program at least once, possibly twice, using Bosch-approved descaler. Scale in the thermoblock or lines can cause pump overpressure and E03.
• Listen to the pump: During a brew attempt, listen for the vibration pump. If it is silent, the pump or its power supply may have failed. If it hums loudly but no water flows, a blockage is likely.
• Advanced check: With covers removed (unplugged), inspect silicone hoses for kinks and check the overpressure valve and outlet valve for visible damage or leaks.
• If unresolved: The ULKA pump or pressure valve assembly may need replacement. This involves disconnecting water lines and electrical connectors; consider professional service.