BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure is too low for the system to run safely.
Why it happens: This fault occurs when the water level inside your central heating system drops too low for the boiler to operate safely. The most common reasons are a slow leak from a radiator valve or pipework, or the air being manually bled from radiators without the pressure being topped back up.
Locate the filling loop (usually a silver flexible hose) underneath the boiler.Slowly open the one or two taps/levers on the filling loop to allow water into the system.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps fully.
Your boiler has stopped working because it cannot light a flame, which is usually caused by a temporary interruption in the gas supply or a component failure.
Why it happens: This fault occurs when the boiler attempts to start but fails to detect a flame after several attempts. The most common reason is a temporary interruption in the gas supply or a build-up of carbon and wear on the components that generate the ignition spark.
Check if other gas appliances (like a cooker) are working to confirm gas is reaching the property.Ensure your gas meter has credit if you use a top-up card.Press the reset button on the boiler control panel to see if it restarts.
Your boiler has switched itself off because it has become too hot inside, likely due to a circulation issue or a temporary blockage.
Why it happens: This fault occurs when the internal temperature of the boiler exceeds safe limits, triggering a safety switch to prevent damage. The most common reasons are a pump failure that stops water from moving or a buildup of debris and limescale that restricts flow through the heat exchanger.
Check that your radiator valves are open to allow water to flow.Check your boiler pressure gauge and top it up to 1.5 bar if it is too low.Let the boiler cool down for 30 minutes, then press the 'Reset' button (the flame symbol with a cross).
Your boiler is struggling to circulate water quickly enough through your pipes, which is causing it to stop to prevent overheating.
Why it happens: This fault occurs when the boiler detects that water isn't moving through the system fast enough to carry heat away from the heat exchanger. The most common reasons are a failing internal pump that has lost its pushing power or a blockage in the narrow pipework that is restricting flow. When the water sits still for too long, it overheats rapidly, forcing the boiler to shut down for safety.
Ensure all radiator valves (TRVs) are fully open to allow water to flow.Check that the boiler pressure is between 1 and 1.5 bar on the gauge.Gently bleed your radiators to remove any trapped air pockets.
Your boiler is failing to light because it isn't receiving a gas supply or cannot detect a flame.
Why it happens: This fault occurs when the boiler's internal computer tries to start the burner but cannot establish a sustained flame. The most common reasons are a temporary interruption in your gas supply, a worn-out ignition probe that cannot create a spark, or a faulty gas valve failing to release fuel into the combustion chamber.
Check that your gas emergency control valve (usually by the meter) is in the 'on' position.If you have a pre-payment meter, check that you have sufficient credit.Check if other gas appliances in the home, such as a hob, are working correctly.Press and hold the reset button for five seconds to see if the boiler restarts.
Your boiler has lost its water pressure, which means it has stopped running to protect the internal components from damage.
Why it happens: This fault occurs when the water level inside your central heating system drops too low for the boiler to operate safely. It is usually caused by a small leak in the pipework or radiators, or because air was recently bled from the system without being topped back up.
Locate the filling loop (usually a silver flexible hose) under the boiler.Slowly open the one or two small taps on the hose until you hear water flowing.Watch the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps tightly.
on the Glow-worm Xtrafast 96
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