BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because it cannot get a steady supply of gas to stay lit.
Why it happens: This fault occurs when the boiler tries to light the flame but fails to detect one, causing the system to shut down for safety. The most common reasons are a temporary interruption in your gas supply, worn-out ignition parts that can no longer create a spark, or a faulty internal valve that isn't opening properly.
Check if other gas appliances, like a cooker, are working to confirm your gas supply is active.If you have a prepayment meter, check that you have enough credit.Locate your gas meter and ensure the main handle is in the 'on' position.Reset the boiler by turning the main selector dial to 'Reset' for five seconds, then back to your preferred setting.
Your boiler has detected a blockage in the exhaust pipe or a problem with the fan, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler's safety sensors detect that harmful exhaust gases are not being cleared from the system effectively. The most common reasons are a mechanical failure of the fan, a blockage in the external flue pipe, or a perished internal seal that is leaking air.
Check the external flue pipe (the white pipe on your outside wall) for any visible obstructions like bird nests, leaves, or debris.Ensure there are no items such as garden furniture or plants blocking the airway of the flue.If the exterior is clear, do not attempt to open the boiler; you must call a Gas Safe engineer to inspect the internal fan and air pressure switch.
Your boiler has detected that there is not enough water in the heating system to operate safely.
Why it happens: This fault occurs when the water pressure inside your heating system drops below a safe level, preventing the boiler from firing up to protect the internal components. The most common reasons for this are a leak somewhere in the pipework or radiators, or simply needing to top up the system after bleeding air from your radiators.
Locate the filling loop (usually a silver flexible hose) underneath or near the boilerSlowly open the tap or taps on the filling loop to allow water into the systemMonitor the pressure gauge until it reaches between 1 and 1.5 bar, then close the taps fully
Your boiler is failing to ignite because it cannot start the small flame needed to fire up the main burner.
Full guide for Pilot will not lightYour boiler has lost all power and is completely unresponsive because it is not receiving an electrical signal.
Full guide for Mains LEDsYour boiler has stopped working because the flame has extinguished unexpectedly, triggering a safety shutdown to prevent gas buildup.
Full guide for Red lockout light Fon the Glow-worm Compact (2006-2011)
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