High
E004 on Navien NCB 40 HE

Your boiler has detected a flame when it shouldn't be burning, suggesting a sensor error or a gas valve issue that prevents the unit from starting safely.

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

False flame detection

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

E003View →E005View →

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