BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has become too hot internally and needs to cool down for safety.
Why it happens: This fault occurs when the water inside the boiler reaches an illegally high temperature, triggering a safety sensor to shut the system down. The most common reason is that the water isn't moving through the unit quickly enough, often due to a pump failure or a blockage caused by sludge buildup in the pipework. It can also happen if there is trapped air in the system or if the internal divertor valve has become stuck.
Check that your radiator valves are open and not turned to the off positionEnsure your boiler pressure is between 1.0 and 1.5 bar on the displayPress the reset button (a flame symbol with a cross through it) once the boiler has cooled down
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Why it happens: This fault occurs when the water pressure inside your heating system drops below the minimum level required for the boiler to fire up safely. The most common reason is a slow leak from a radiator valve or pipework, though it can also happen if you have recently bled your radiators and haven't topped the pressure back up.
Locate the filling loop (a flexible silver hose) underneath or near the boiler.Slowly open the one or two taps on the hose until you hear water flowing.Watch the pressure gauge and close the taps once the needle reaches between 1.0 and 1.5 bar.
Your boiler has shut down because the water is heating up too quickly or unevenly, suggesting a circulation problem.
Why it happens: This fault occurs when the boiler's internal sensors detect that water is heating up too fast or that there is a massive temperature gap between the water leaving and returning to the unit. The most common reason is a pump failure or a blockage that prevents water from moving through the system quickly enough to carry the heat away. It can also be caused by air trapped in the heat exchanger or a buildup of limescale restricting the flow.
Ensure all radiator valves (TRVs) are turned to the highest settingCheck that the boiler pressure is between 1.0 and 1.5 bar on the displayGently bleed air from your radiators using a radiator key
Your boiler has shut down because the water inside is heating up much faster than it can be moved around the system, usually due to a blockage or a pump issue.
Why it happens: This fault occurs when the heat exchanger gets too hot because the water isn't flowing away from it quickly enough. The most common reasons are a failing pump that can't push the water through or a build-up of sludge and debris blocking the internal pipework. In some cases, it can also be caused by air trapped in the system or a faulty sensor misreading the temperature.
Ensure all radiator valves (TRVs) are fully openCheck that the boiler pressure is between 1.0 and 1.5 barPress the reset button once to see if the fault clears
Your boiler has tried to light the gas but failed, meaning it cannot provide heating or hot water until reset.
Why it happens: This fault occurs when the boiler attempts to ignite the gas three times but fails to detect a flame. The most common reasons are a temporary interruption in your gas supply, a blocked burner, or an issue with the electrodes that create the spark needed for ignition.
Check that your gas meter has credit and the isolation valve is openPress the Reset button (the flame symbol with a cross) for one secondCheck if other gas appliances in your home, like a hob, are working correctly
Your boiler was lit but the flame has gone out unexpectedly, which has caused the system to stop working for safety.
Why it happens: This fault occurs when the boiler successfully ignites but cannot maintain the flame, leading the system to shut down for safety. The most common reasons include an inadequate gas supply, debris on the burner, or a faulty sensor that can no longer detect that the flame is actually lit.
Check that your gas emergency control valve is open and you have credit on your gas meterPress the 'Reset' button (indicated by a flame with a cross through it) for five secondsDuring freezing weather, check if your external white plastic condensate pipe has frozen and thaw it with warm water
on the Glow-worm Energy
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