Breville espresso machine shows ER04 and stops brewing mid-cycle.

Safety: Unplug the machine and allow it to cool. Hot water and steam under pressure can cause burns.

User-level checks:

• Check water supply: Ensure the tank is full, properly seated, and the intake filter is not clogged.
• Backflush (if 3-way solenoid model): Use a blind filter and Breville-approved cleaning tablet to backflush the group head and solenoid valve.
• Descale thoroughly: Run a complete descale cycle to clear scale from the thermoblock and internal passages.

Advanced diagnostics:

• Listen for the ULKA pump during a brew attempt. A loud buzzing with no water flow suggests a blockage; silence suggests a failed pump or power issue.
• Remove the shower screen and group head screw; clean any coffee oils and fines blocking the dispersion plate.
• Inspect the OPV and associated tubing for blockages or kinks (requires opening the case).

Resolution: If descaling and cleaning do not restore normal operation, replace the ULKA pump and inspect/clean the OPV. Persistent ER04 after pump replacement may indicate a faulty pressure sensor or control board, requiring professional service.