High
C 20 on Atag S 25CR

Your boiler is currently unable to detect the flow of water because the sensor responsible for monitoring it is providing an incorrect reading or has stopped communicating with the system, which will prevent your heating and hot water from working.

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 sensor error (e.g. open, short circuit, outside of range)

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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