BoilerFaultCodesThe 6 most common faults
Your boiler is failing to light the gas to create a flame, meaning you have no heating or hot water.
Why it happens: This fault occurs when the boiler tries to start up but cannot successfully light the gas or detect that a flame is present. The most common reasons include a worn-out ignition spark, a faulty gas valve that isn't opening properly, or an issue with the main control board failing to send the right signals.
Check if your gas supply is active by testing other gas appliances like a hob.Check if your gas meter has credit (if using a pre-payment meter).Press the reset button (indicated by a flame with a line through it) for five seconds.
Your boiler started to light but the flame went out unexpectedly while it was running, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler successfully starts but cannot maintain a steady flame, causing the system to shut down for safety. It is usually caused by a dirty or worn-out sensing probe that can no longer 'see' the fire, or a faulty gas valve that isn't providing a consistent flow of fuel. In some cases, a build-up of carbon or debris on the burner can also interfere with the combustion process.
Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is active.Check if your prepaid gas meter has credit.Reset the boiler by pressing the reset button or turning it off and on again.
Your boiler has switched itself off because it has gotten too hot, likely due to a circulation issue or a component failure.
Why it happens: This fault occurs when the water inside the boiler reaches an unsafe temperature, triggering a safety sensor to shut the system down to prevent damage. The most common reasons are a failed pump that isn't moving water away from the heat exchanger quickly enough, or a blockage caused by a build-up of debris and sludge within the system.
Check that all radiator valves are fully openCheck that the boiler pressure is between 1.0 and 1.5 bar on the gaugeWait 30 minutes for the unit to cool down and try pressing the reset button
Your boiler has tried to ignite but failed, likely because gas isn't reaching the burner or the flame isn't being detected.
Why it happens: This fault occurs when the boiler attempts to start up but cannot successfully establish or detect a flame. The most common reasons are a lack of gas reaching the unit, a build-up of carbon on the ignition probes, or an internal component like the gas valve failing to open.
Check if other gas appliances in your home, like a hob, are working to confirm gas supply.If you have a pre-payment meter, ensure you have sufficient credit available.Press the 'Reset' button (often indicated by a flame with a cross through it) to see if the boiler restarts.
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Why it happens: This fault occurs when the internal temperature of the boiler exceeds safe limits, triggering a safety sensor to cut the power. It is usually caused by a lack of water flow, often due to a pump failure or a blockage in the main heat exchanger that prevents heat from being carried away from the burner.
Turn the boiler off and allow it to cool for 20 minutesCheck that your radiator valves are open and not turned to zeroPress the reset button (usually marked with a flame or 'reset' symbol) to restart the unit
Your boiler has shut down because the water inside it has become too hot, triggered by a safety sensor to prevent damage.
Why it happens: This fault occurs when the water inside the boiler exceeds a safe temperature limit, causing the safety sensors to shut the system down. It is usually caused by a failure to move heat away from the burner, often due to a broken internal pump or a blockage in the pipework. In some cases, a build-up of limescale or sludge can restrict water flow, leading to rapid overheating.
Check that your radiator valves are open and not turned to zero.Ensure there is enough water pressure by checking the gauge is between 1 and 1.5 bar.Wait 15 minutes for the unit to cool down and try pressing the reset button.
on the Glow-worm Ci 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