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 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 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
Your boiler has shut down because the water is heating up too quickly or hasn't been able to circulate correctly through the system.
Why it happens: This fault occurs when the internal sensors detect that water inside the boiler is getting too hot too quickly, or there is too large a temperature difference between the water leaving and returning to the unit. The most common reason is a lack of water flow, often caused by a failing pump or a blockage in the pipework that prevents heat from being carried away to your radiators. It can also be triggered if the sensors themselves become faulty and provide inaccurate temperature readings to the control board.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barSwitch the boiler off and back on again to reset the system
Your boiler has failed to light the gas flame after several attempts, which means you will not have any heating or hot water until it is fixed.
Why it happens: This fault occurs when the boiler tries to light the gas to start the heating process but fails to detect a flame within seven seconds. The most common reasons are a lack of gas supply reaching the unit, a worn-out component that creates the spark, or a fault within the internal valve that controls the flow of fuel.
Check that your gas emergency control valve is in the open positionEnsure any other gas appliances in the home are working to confirm gas supplyIf you have a prepayment meter, check that it has sufficient creditPress the reset button (indicated by a flame with a cross through it) once
Your boiler has shut down because it is getting too hot inside, likely due to water not flowing properly through the system.
Why it happens: This fault occurs when water cannot circulate through the boiler quickly enough to carry heat away, causing the internal temperature to reach a dangerous level. The most common reasons are a seized internal pump that has stopped spinning or a blockage within the pipework, such as trapped air or closed valves. This trigger is a safety mechanism designed to protect the boiler's internal components from heat damage.
Check that all valves (isolating cocks) underneath the boiler are in the open position.Bled all your radiators to ensure there is no trapped air in the system.Ensure the boiler pressure is topped up to between 1 and 1.5 bar.
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
Avoid the next call-out bill
Monthly cover means no unexpected bills when your boiler breaks down.
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