BoilerFaultCodesThe 6 most common faults
Your boiler has failed to light because it isn't receiving gas or the spark isn't igniting the fuel.
Why it happens: This fault occurs when the boiler attempts to start up but fails to detect a flame after several attempts. The most common reasons are a lack of gas supply reaching the unit, a worn-out spark electrode that can no longer ignite the fuel, or a faulty gas valve that isn't opening correctly.
Check that your gas prepayment meter has credit (if applicable).Ensure your gas stopcock and other gas appliances like hobs are working.Press the Reset button (indicated by a flame with a cross through it) on the boiler control panel.
Your boiler has tried to light several times but cannot establish a flame, meaning you will have no heating or hot water until it is fixed.
Why it happens: This fault occurs when the boiler's control system attempts to light the burner but fails to detect a stable flame after several attempts. It is often caused by worn-out ignition sparks that can no longer bridge the gap, a faulty gas valve preventing fuel from entering the burner, or a problem with the internal electronics that monitor the flame.
Check if other gas appliances, like a hob, are working to confirm your gas supply is active.If you have a pre-payment meter, check that you have enough credit.Check that your external condensate pipe hasn't frozen if it is very cold outside.Try resetting the boiler by pressing the 'Reset' button (the flame symbol with a cross).
Your boiler has shut down because its internal temperature has risen too high, usually due to a lack of water flow or a circulation blockage.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature, triggering a safety shutdown to prevent damage. The most common reason is a failure of the internal pump to move water through the heat exchanger, or a blockage caused by a build-up of debris and sludge within the system.
Check that your boiler pressure is between 1.0 and 1.5 bar on the gauge; top up if low.Ensure all radiator valves and isolation valves under the boiler are fully open.Wait 30 minutes for the unit to cool down, then press the reset button (usually marked with a flame or 'reset').
Your boiler has lost water pressure and has shut down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the water level inside your central heating system drops below the minimum level required for the boiler to operate safely. The most common reasons are a slow leak from a radiator valve or pipework, or the air pressure inside the internal expansion vessel needs topping up.
Locate the filling loop (usually two silver braided hoses) beneath the boiler.Gradually open the small black taps until you hear water entering the system.Watch the pressure gauge and close the taps once the needle reaches 1.5 bar.
Your boiler has stopped working because it cannot light the gas burner to provide heating or hot water, usually because the gas supply is interrupted or the ignition spark has failed.
Why it happens: This fault occurs when the boiler attempts to light but fails to detect a flame after several tries, forcing the system into a safety shutdown. The most common reasons are an interruption in the gas supply, a build-up of carbon on the ignition probes, or a component failure that prevents the spark from starting the fire.
Check if your gas meter has credit or if other gas appliances in your home are working.Ensure the blue gas isolation valve under the boiler is in the 'open' position (aligned with the pipe).Press the 'Reset' button (indicated by a flame with a line through it) and hold for one second.
Your boiler has stopped working because it cannot light the gas needed to provide heating and hot water.
Why it happens: This fault occurs when the boiler attempts to start up but fails to sense a flame after several attempts. The most common reasons are a lack of gas reaching the unit, a dirty ignition electrode that can no longer spark, or a faulty gas valve failing to open.
Check if your gas supply is turned on at the meterCheck if other gas appliances, like a hob, are working correctlyPress the reset button (indicated by a flame with a line through it) for five seconds
on the Glow-worm 30ci Plus
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