BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system is too low to run safely.
Locate the external filling loop, usually two silver flexible hoses with valves beneath the boiler.Slowly open the valves to allow mains water to enter the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valves tightly and check for any signs of leaking.
Your boiler has switched off because the internal water pressure has dropped too low to operate safely.
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.
Your boiler has detected that it is running out of water inside its internal system, which prevents it from heating your home safely.
Locate the external filling loop, usually a silver flexible hose connected to two valves under the boiler.Gradually open the valves to allow water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valves tightly and restart the boiler.
Your boiler has detected an issue with the water pressure level, which is causing it to stop operating to prevent damage.
Locate the filling loop under the boiler, which is usually a silver braided hose or a small plastic key.Open the valve(s) slowly to allow mains water into the system until the pressure gauge on the front of the boiler reads between 1.0 and 1.5 bar.Close the valve(s) tightly and restart the boiler using the reset button.
Your boiler has stopped working because the water pressure inside the heating system has dropped below the required level.
Locate the filling loop (a flexible metal hose) connected to the pipes underneath your boiler.Open the valves on the filling loop to allow cold mains water into the system.Watch the pressure gauge on the boiler until the needle reaches the green zone (usually between 1 and 1.5 bar) and then firmly close both valves.
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 E001on the Navien NCB
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