BoilerFaultCodesThe 6 most common faults
Your boiler is failing to light the flame needed to heat your water and radiators.
Why it happens: This fault occurs when the boiler attempts to start up but cannot confirm that a flame has been successfully lit. The most common reasons are that the spark isn't reaching the burner, the sensor that detects the heat is dirty or worn out, or the gas valve isn't opening correctly to provide fuel.
Check that your gas pre-payment meter hasn't run out of creditEnsure other gas appliances in your home, like a hob, are receiving gasPress the 'Reset' button on the boiler control panel to see if it restarts
Your boiler has got 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 rises above a safe limit, causing it to trip a safety switch. The most common reasons are a failed pump that isn't moving water around the system quickly enough, or a blockage caused by sludge and debris inside the heat exchanger. It can also be caused by an air lock in the pipework that prevents the water from absorbing the burner's heat.
Check that all radiator valves are fully open (especially TRVs)Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar)Press the reset button once the boiler has had time to cool down
Your boiler has stopped working because the fan system cannot properly clear waste gases or bring in fresh air to burn fuel safely.
Why it happens: This fault occurs when the boiler's internal safety sensors detect that the fan isn't moving enough air to safely vent exhaust gases outside. The most common reasons are a build-up of dirt in the fan assembly, a blockage in the flue pipe, or a failure in the electronic switch that monitors air pressure.
Full guide for 02Your boiler has detected a problem with the internal sensor that monitors the temperature of your heating water, meaning the system cannot run safely.
Why it happens: This fault occurs when the boiler's control board loses communication with the sensor that measures the temperature of the water in your radiators. The most common reason is that the sensor has physically failed or 'drifted' out of its correct electrical range, but it can also be caused by loose or corroded wiring connections between the sensor and the main circuit board.
Full guide for 06Your boiler has lost its ability to monitor the temperature of the stored hot water, meaning it cannot heat your water reliably or safely.
Why it happens: This fault occurs when the sensor responsible for monitoring the temperature inside the boiler's internal hot water storage tank fails or loses its connection. The most common reason is that the sensor has physically degraded over time or the electrical wiring has become loose or corroded, preventing the control board from knowing if the water is hot or cold.
Full guide for 08Your boiler's internal sensor is struggling to accurately read the water pressure, which prevents the system from operating safely.
Why it happens: This fault occurs when the electronic sensor responsible for monitoring the water level inside the boiler fails or provides an illogical reading. The most common reason is that the sensor's internal diaphragm has become blocked with system sludge or the electrical connections have corroded over time. Because the boiler cannot confirm there is enough water to operate safely, it shuts down to prevent internal overheating.
Full guide for 09on the Glow-worm Xtrafast 96 120
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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