BoilerFaultCodesThe 5 most common faults
Your boiler has lost power or has insufficient water pressure to operate, meaning it cannot provide heating or hot water.
Why it happens: This fault occurs when the boiler's control system fails to detect either electrical power or sufficient water pressure to safely ignite. The most common reasons are a blown internal fuse on the circuit board or a leak in the system that has caused the pressure to drop below the minimum required level.
Check that the main power switch for the boiler is turned onCheck your home's fuse box / consumer unit for any tripped switchesIf your system has a pressure gauge, check if it is below 1.0 bar and top it up using the filling loop
Your boiler has detected that the water pressure is too low to operate safely and has shut down to prevent damage.
Why it happens: This fault occurs when the water inside your heating system drops below the minimum level required for the boiler to heat up safely. The most common reasons for this are a leak somewhere in your radiator pipework or the water expansion vessel losing its internal air pressure over time.
Locate the filling loop, which is usually a silver flexible hose with two small valves.Slowly open both valves to allow fresh water into the system.Watch the pressure gauge and close both valves tightly once it reaches between 1.0 and 1.5 bar.
Your boiler has switched itself off to prevent overheating because the system is getting too hot or the water is not circulating properly.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety switch to shut the system down. The most common reasons are a pump that has stopped circulating water or a blockage in the pipework that prevents heat from escaping the boiler. Just like an engine overheating, the boiler stops to prevent internal damage to its components.
Full guide for Neon 2 NOT litYour boiler has detected that the internal safety fan isn't moving air properly, so it has shut down for safety.
Why it happens: This fault occurs when the boiler's internal computer sends power to the fan but does not receive a signal back confirming that air is moving through the flue. The most common reasons are a motor failure within the fan itself or a blockage in the small plastic tubes that sense air pressure. Without this confirmed airflow, the boiler cannot safely light the flame and will stay in a safe mode.
Full guide for Neon 3 NOT litYour boiler is failing to light the pilot flame or detect a steady flame, meaning it cannot start the heating process.
Why it happens: This fault occurs when the boiler attempts to start up but cannot establish or maintain the small pilot flame needed to ignite the main burner. The most common reasons are a blocked pilot hole preventing gas flow or a worn-out sensor that can no longer tell the boiler it is safe to stay on. In some cases, the gas valve may be failing to release the fuel required to start the ignition process.
Full guide for Neon 4 NOT liton the Glow-worm Space Saver Compleheat 30 40 50
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 Glow-worm 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