BoilerFaultCodesNavien 98 Fault Code
The Navien 98 fault code means: your boiler is having trouble communicating with an internal control board responsible for managing extra heating system features, which may prevent your heating or hot water from working correctly.. It appears on 1 Navien model in our database.
Technical description: Extension module 1: Fault extension module 1
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 98 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Navien 98 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