BoilerFaultCodesNavien 118 Fault Code
The Navien 118 fault code means: your boiler has stopped working because the amount of water circulating inside the system has dropped below the required level.. It appears on 1 Navien model in our database.
Technical description: Water pressure too low: Dry fire protection: Water pressure too low
DIY fix possible
Locate the filling loop (a metal braided hose) situated underneath the boiler.Open the valves on the filling loop slowly until you hear water flowing.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (typically 1.0 to 1.5 bar).Close both valves firmly and ensure the boiler resets.
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Navien models that show the 118 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Navien 118 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