High Lockout
918 on Ideal Ideal Classic SE15P FF

Your boiler has shut down because the water inside it has become too hot, which is often caused by a blockage or a pump that isn't moving water through the system correctly.

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 inside the boiler exceeds a safe temperature limit, causing the system to shut down for safety. The most common reasons are a failed pump that isn't circulating the water, or a physical blockage like limescale or sludge that is stopping the heat from escaping the boiler.

This issue often surfaces during the first cold spell of autumn when a pump that has been idle all summer fails to restart.

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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