Error 10; unit indicates overpressure or abnormal pressure reading in the primary circuit.

Safety: Let the system cool. High pressure can cause hot water discharge from the safety valve.

• Check pressure gauge: If pressure is above the recommended limit (e.g., >2.5–3 bar), carefully bleed water from a radiator or drain point to reduce pressure.
• Test expansion vessel: With the system depressurized, check the air charge at the expansion vessel Schrader valve using a tire gauge. If no air or water comes out, the vessel may be failed and should be replaced or recharged to the specified pressure.
• Inspect pressure sensor: Ensure the sensor port is not blocked by sludge. Clean or replace as needed.
• Reset and monitor: After correcting pressure, reset the unit and monitor for recurring pressure rise, which indicates an expansion vessel or filling loop issue.

Note: Expansion vessel replacement is typically a technician task due to system draining and re‑commissioning requirements.