BoilerFaultCodesThe 6 most common faults
01
E302 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
What to try first
Locate the external filling loop, which is a flexible braided hose usually found underneath the boilerOpen the valves at both ends of the filling loop to let mains water into the systemMonitor the pressure gauge on the front of the boiler until the needle reaches between 1.0 and 1.5 barClose both valves tightly and remove the filling loop if required by your specific model
02
001 High Engineer
Your boiler has detected an internal issue where the fan is not spinning at the required speed to safely exhaust gases.
Full guide for 00103
003 High Engineer
Your boiler has failed to ignite because it was unable to sense a flame after starting up.
Full guide for 00304
004 High Engineer
Your boiler has detected a failure to ignite the flame, meaning it is currently unable to provide heating or hot water.
Full guide for 00405
012 High Engineer
Your boiler has detected that it is not receiving enough water flow to operate safely and has shut itself down to prevent damage.
Full guide for 01206
016 High Engineer
Your boiler has detected that it is overheating and has shut itself down to prevent any damage to the internal parts.
Full guide for 016on the Navien NCB CE
Filling loopPressure relief valvePressure sensorFan assemblyWiring harnessPCB
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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