High Lockout
E23 on Ravenheat Csi Primary

Your boiler has detected a fault with the sensor that monitors exhaust gases, and as a safety precaution, it will not operate until this is fixed.

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 sensor damaged

What causes this fault?

This fault occurs when the internal sensor responsible for monitoring the temperature of the exhaust gases becomes faulty or disconnected. The most common reason is natural wear and tear or heat damage to the sensor's thermistor, which prevents it from sending an accurate reading to the main control board. As a safety measure, the boiler shuts down to prevent any risk of the flue system overheating.

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

E05View →E24View →

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