High
B 24 on Keston C40

Your boiler has detected that hot water is moving in the wrong direction or the sensors are misreading the temperature, causing the system to stop working to protect itself.

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.

What the manual says

Manufacturer manual

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

From this model's manual
Verified against the Keston C40 installation & service manual, page 31.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

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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B 25View →B 26View →

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