E788 Emergency

Navien E788 Fault Code

The Navien E788 fault code means: your boiler has detected an issue with the way it is managing its gas supply, meaning it has safely shut itself down to prevent it from operating incorrectly.. It appears on 4 Navien models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: Abnormal Gas Setting
Typical repair cost £150-300 (including labour)

Engineer required

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

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Navien models that show the E788 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Navien E788 fault code information on this page is sourced and cross-checked against the official Navien service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026