High Lockout
H9 on Ideal Mexico HE

Your boiler has sensed that the exhaust gases are getting too hot and has shut down as a safety precaution to prevent internal damage.

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 OVERHEAT

What causes this fault?

This fault occurs when the internal temperature of the exhaust fumes exceeds a safe limit, triggering an emergency shutdown to protect the boiler's components. The most common reason is a build-up of limescale or debris inside the heat exchanger, which prevents heat from being transferred to your water and instead sends it out through the flue. It can also be caused by a faulty sensor giving an incorrect reading or a blockage in the system's circulation.

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

L9View →

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