BoilerFaultCodesNavien E302 Fault Code
The Navien E302 fault code means: your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.. It appears on 8 Navien models in our database.
Technical description: The pressure is lower than the minimum pressure set (0.4 bar by default)
DIY fix possible
Locate the external filling loop, which is a flexible silver hose connected to two valves under your boiler.Open both taps on the filling loop slowly to let water into the system while watching the pressure gauge.Close both taps firmly once the needle sits in the green zone, typically between 1.0 and 1.5 bar.
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Gas Safe Register →Navien models that show the E302 fault code
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Source
Navien E302 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 27 April 2026