High Lockout
918 on Ideal Response SE

Your boiler has shut down because it has detected that the water inside is getting too hot, which is often caused by a blockage or a pump failure.

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

Maximum temperature - Flow temperature T1 too high

What causes this fault?

This fault occurs when the water leaving the boiler exceeds its safe temperature limit, causing the system to shut down to prevent damage. It is usually caused by a failure in the circulation pump or a physical blockage within the internal pipework that stops heat from moving away from the burner. In some cases, a faulty sensor may also be incorrectly reporting that the water is overheating.

This issue is frequently seen when the heating is first turned on after summer, as the circulation pump can seize up after long periods of inactivity.

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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