High Lockout
925 on Ideal Response SE

Your boiler is overheating because the water inside is heating up too quickly, often caused by a lack of circulation or a blockage.

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 increase too fast

What causes this fault?

This fault occurs when the water inside the boiler heats up at an unsafe speed, causing the system to shut down to prevent damage. The most common reason is that the water isn't moving through the unit properly, often due to a pump failure, trapped air, or a buildup of sludge blocking the pipework.

This issue often surfaces when the heating is turned back on after summer, as circulation pumps can seize if they haven't been used for several months.

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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