BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system has dropped too low.
Locate the external filling loop, which is a silver braided hose connecting two pipes near your boiler.Open the valves on both ends of the filling loop to allow water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (typically 1.5 bar).Close both valves tightly to stop the flow of water and check for any leaks.
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
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
Your boiler has detected an internal issue where the fan is not spinning at the required speed to safely exhaust gases.
Full guide for 001Your boiler has failed to ignite because it was unable to sense a flame after starting up.
Full guide for 003Your boiler has detected a failure to ignite the flame, meaning it is currently unable to provide heating or hot water.
Full guide for 004Your 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 012on the Navien NCB CE
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