BoilerFaultCodesThe 6 most common faults
Your boiler has detected that the water pressure inside the heating system is too high for it to operate safely.
Locate a radiator in your home with a bleed valveOpen the valve using a radiator key to release a small amount of water into a clothCheck the boiler pressure gauge until it drops into the green zone (usually between 1.0 and 1.5 bar)Close the radiator bleed valve tightly
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
Locate the internal filling loop (usually a silver braided hose or a plastic linkage under the boiler).Slowly open the valves to allow mains water into the system until the pressure gauge reads between 1.0 and 1.5 bar.Close the valves firmly and ensure no water is leaking from the connection points.
Your boiler has been trying to refill its internal water supply for too long but has failed to reach the required level.
Full guide for E351Your boiler has detected that the water temperature inside is getting dangerously high and has shut itself down to prevent damage or overheating.
Full guide for E001Your boiler has failed to light the flame needed to heat your water and home.
Full guide for E003Your boiler has detected a flame when it shouldn't be burning, suggesting a sensor error or a gas valve issue that prevents the unit from starting safely.
Full guide for E004on the Navien NCB H
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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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