Medium
E788 on Navien NCB500

Your boiler has detected an accidental attempt to change the gas setting on the control panel, which prevents it from operating for safety reasons.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

What the manual says

Manufacturer manual

Error code that appears if you try to change the gas type on the front panel

Shared across the NCB500 range
This code is shared by the boilers in this range, which use the same control board. It may not be printed in this exact variant’s manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

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

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All 52 fault codes on the NCB500

Seeing a different code? Every code this model can display, in one place.

001003004012016030031046047109205218302352353515517593594615740782E001E003E004E012E016E030E031E046E047E109E110E205E218E291E302E351E352E353E480E515E517E593E594E598E615E740E782E783E787

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