BoilerFaultCodesThe 6 most common faults
01
E302 High DIY-safe
Your boiler has temporarily stopped working because the water pressure inside the system has dropped too low.
What to try first
Locate the filling loop valves underneath your boiler.Open the valves gently to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valves tightly and check the digital display to see if the error clears.
02
001 High Engineer
Your boiler has detected an internal communication error and has safely shut itself down as a precaution.
Full guide for 00103
003 High Engineer
Your boiler has failed to light the flame properly and has stopped attempting to heat your home or water for safety reasons.
Full guide for 00304
004 High Engineer
Your boiler has detected a false flame signal, meaning the system thinks the burner is lit when it should be turned off.
Full guide for 00405
012 High Engineer
Your boiler has detected that it is not receiving enough water flow to operate safely or effectively.
Full guide for 01206
016 High Engineer
Your boiler has detected an issue related to the flow of water inside the unit, which has caused it to stop working to protect itself from potential overheating.
Full guide for 016on the Navien NCB300
Pressure sensorFilling loop valveExpansion vesselMain PCBCommunication wiring harnessIgnition electrode
Based on parts cited in our fault code database. Your engineer will confirm what's actually needed after diagnosis.
Call a Gas Safe engineer if…
- You can smell gas or see signs of a leak
- The Navien shows an Emergency or High severity code
- The boiler keeps locking out after repeated resets
- You've tried the DIY checks and the fault hasn't cleared
- There's visible water leaking from the boiler
- The flame is yellow or orange instead of blue
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