High Lockout
E03 on Remeha Avanta 18V

Your boiler has shut down because it detected that the exhaust gases are getting too hot, which is a safety measure to protect the internal components.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description

Flue gas thermostat exceeded

What causes this fault?

This fault occurs when the internal heat exchanger becomes blocked with debris or limescale, preventing heat from being transferred to the water effectively. As a result, excessive heat escapes through the flue system, causing the safety sensor to trip and shut down the boiler to prevent melting or fire damage. The most common reason is a lack of annual servicing, which allows buildup to restrict the airflow and heat transfer within the unit.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

E01View →E10View →E13View →

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