High
E353 on Navien NCB

Your boiler has detected that water is leaking internally or not heating up as expected within its hot water system.

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

Water leaks or low temperature water in the heat exchanger (DHW Heat Exchanger).

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

E351View →E352View →

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