High
B 24 on Keston C90 / C110

Your boiler has detected that hot water is flowing in the wrong direction, indicating a potential issue with your heating system's pump or sensor wiring.

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

Return temperature exceeded flow temperature. Check pump direction on boiler and any external pumps. Check wires on flow and return thermistors are not crossed.

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

B 25View →B 26View →

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