High Lockout
E5218 on Worcester Bosch Greenstar Si Combi / i System

Your boiler has shut down because the internal water temperature has become too hot, likely due to a lack of water flow or a circulation problem.

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

Flow temperature too high

What causes this fault?

This fault occurs when the water inside the boiler heats up too quickly or reaches an unsafe temperature, forcing the system to shut down for safety. The most common reason is a failure in the circulation pump or a blockage in the pipes, which prevents the hot water from moving away from the burner. It can also be caused by a faulty sensor that is incorrectly reporting the water temperature to the control board.

This issue often appears when the heating is first turned on after summer, as circulation pumps can seize up 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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Related fault codes

E9 224View →

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