BoilerFaultCodesThe 6 most common faults
01
E02 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 filling loop (usually two silver flexible hoses) underneath the boiler.Open the valves slowly to allow mains cold water into the system.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 tightly to stop the flow of water.
02
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 00303
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 01604
060 High Engineer
Your boiler has detected an issue with the air supply or exhaust system, meaning it cannot operate safely and has shut down to prevent damage.
Full guide for 06005
205 High Engineer
Your boiler has detected an issue with the air flowing through the flue system, causing it to shut down for safety.
Full guide for 20506
110 Emergency Engineer
Your boiler has detected that it is not effectively removing waste gases produced during the heating process, causing it to shut down for safety.
Full guide for 110on the Navien NCB-34LDWE
Filling loopPressure relief valveExpansion vesselIgnition electrodeGas valveFlame sensor
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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