BoilerFaultCodesThe 6 most common faults
01
E302 High DIY-safe
Your boiler has switched off because the internal water pressure has dropped too low to operate safely.
What to try first
Locate the external filling loop, usually a silver braided hose near the boiler pipes underneath.Open the valves at both ends of the filling loop to allow water to enter the system.Monitor the boiler pressure gauge until it reaches the green zone, typically between 1.0 and 1.5 bar.Close both valves tightly and remove the filling loop if required by your specific model.
02
E001 High Engineer
Your boiler has detected that it is getting too hot and has automatically shut down to prevent damage to its internal parts.
Full guide for E00103
E003 High Engineer
Your boiler is failing to light the flame properly, so it has stopped trying to prevent gas from building up inside.
Full guide for E00304
E012 High Engineer
Your boiler has stopped because the flame inside has gone out and will not stay lit, meaning you currently have no heating or hot water.
Full guide for E01205
E016 High Engineer
Your boiler has detected that the water inside it is getting dangerously hot and has shut itself down to prevent damage or overheating.
Full guide for E01606
E030 High Engineer
Your boiler is overheating because it cannot effectively transfer heat to your water, likely due to a build-up of internal mineral deposits.
Full guide for E030on the Navien NCB
Filling loopPressure relief valveExpansion vesselCentral heating pumpFlow sensorHeat exchanger
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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