High
C 40 on Atag S 25CR

Your boiler is struggling to accurately measure the temperature of the water returning to it, which prevents the system from heating your home correctly.

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 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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