Low
E740 on Navien NCB 40 HE

Your boiler is struggling to read the temperature outside, which means it cannot automatically adjust your heating to match the weather conditions.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Abnormal operation: outdoor temperature sensor (appears only when the outdoor reset curve is enabled).

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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