291 High

Navien 291 Fault Code

The Navien 291 fault code means: your boiler has detected an electrical problem or overheating issue near its internal safety seals, causing it to shut down to prevent damage.. It appears on 1 Navien model in our database.

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: 291:WCS overt + G83: Water cooled seal thermostat has operated and G83/ENS module has detected an unhealthy mains condition, or if GIM fitted, an over-voltage event has occurred
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 291 fault code

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

Source

Navien 291 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