BoilerFaultCodesThe 6 most common faults
Your boiler has tried to light itself several times but has been unable to produce a flame, meaning your heating and hot water will not work.
Why it happens: This fault occurs when the boiler's internal computer signals for heat but the burner fails to sustain a flame after multiple attempts. The most common reasons include a lack of gas reaching the unit, a worn-out ignition spark plug, or a sensor that can no longer detect when the fire is lit.
Check if your gas supply is active, perhaps by testing a gas hob or checking your prepaid meter credit.Look for any frozen external pipes (condensate pipe) and gently thaw with warm water if needed.Press the reset button (indicated by a flame with a line through it) for five seconds.
Your boiler is shutting down because it is getting too hot too quickly, likely due to a water circulation problem.
Why it happens: This fault happens because water is not moving through the boiler fast enough to carry heat away, causing the internal temperature to spike instantly. The most common reasons are a broken internal pump that can't push the water or a buildup of sludge and scale that has physically blocked the narrow channels inside the heat exchanger.
Check that your radiator valves are openEnsure the system pressure is between 1.0 and 1.5 barGently bleed your radiators to remove trapped air
Your boiler started to heat up but the flame went out unexpectedly, causing the system to shut down for safety.
Why it happens: This fault occurs when the boiler successfully lights but then loses its flame while it is supposed to be running. It is often caused by a dirty or worn-out sensor that can no longer 'see' the flame, or by an unstable gas supply that prevents the fire from staying lit. In some cases, internal debris or a failing control board can also interrupt the combustion process.
Check that your gas emergency control valve is open and other gas appliances are working.Verify if you have credit on your prepaid gas meter.Press the reset button (indicated by a flame with a line through it) to see if the boiler restarts.
Your boiler has detected an issue with its internal sensor that monitors water pressure, preventing it from heating up.
Why it happens: This fault occurs when the boiler's control board loses communication with the sensor that monitors internal water pressure. The most common reason is that the sensor has developed an electrical failure or has become blocked with system debris, preventing it from sending a steady signal. In some cases, the issue is caused by loose or damaged wiring connecting the sensor to the main computer.
Check the pressure gauge on the front of the boiler is between 1.0 and 1.5 barIf the pressure is low, use the filling loop underneath to top the system upReset the boiler using the power or reset button to clear the fault
Your boiler has switched itself off because the water pressure is too low for it to operate safely.
Why it happens: This fault occurs when the system loses the physical water pressure required to circulate heat around your home. The most common reason is a small leak in the radiator network or the boiler's internal components, though it can also happen if you have recently bled your radiators without topping the water back up.
Locate the filling loop (usually a silver braided hose with small valves) underneath the boiler.Slowly open the valves until you hear water moving and watch the pressure gauge.Close both valves tightly once the pressure needle reaches between 1.0 and 1.5 bar.
Your boiler has stopped working because the water isn't moving through the system correctly, which is often caused by air bubbles or a blockage.
Why it happens: This fault occurs when the boiler detects a significant temperature difference between the water leaving the unit and the water returning to it, indicating that heat is not being carried away fast enough. The most common reasons are a failing internal pump that can't push the water around, or a build-up of sludge and debris that has created a physical blockage in the pipework. It can also be triggered by a large pocket of air trapped within the heat exchanger, preventing smooth water flow.
Check that all radiator valves and isolation valves are fully openBleed your radiators to remove trapped air from the systemCheck the boiler pressure gauge and top it up to 1.5 bar if it is too low
on the Glow-worm Xtramax HE
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