BoilerFaultCodesThe 6 most common faults
Your boiler has failed to ignite and is not producing heat, which is usually due to an interrupted gas supply or a problem with the internal spark system.
Why it happens: This fault occurs when the boiler tries to light the flame but fails to detect one, causing the system to shut down for safety. The most common reasons are a temporary interruption in the gas supply, a build-up of carbon on the ignition probes, or a component failure that prevents the spark from starting the combustion process.
Check if other gas appliances, like a cooker, are working to confirm gas is reaching the propertyEnsure your gas meter has credit if you use a pre-payment accountPress the reset button (indicated by a flame with a line through it) and hold for two seconds
Your boiler is failing to light the flame properly, which means it cannot heat your radiators or water.
Why it happens: This fault occurs when the boiler's control system attempts to start a flame but fails to detect one after several attempts. The most common reasons are a lack of gas reaching the burner, worn-out ignition sparks that can no longer bridge the gap, or a carbon-coated sensor that cannot 'see' the flame once it has lit.
Check if your gas supply is turned on at the meterCheck if other gas appliances in your home are working correctlyPress the reset button (flame symbol with a cross) for one second
Your boiler has got too hot and has automatically shut down for safety to prevent damage.
Why it happens: This fault occurs when the internal water temperature rises too quickly or exceeds a safe limit, causing the boiler to shut down to prevent internal damage. The most common reasons are a failed pump that isn't moving water away from the heat exchanger fast enough, or a build-up of debris causing a blockage in the pipework. It can also be triggered if air is trapped in the system or if the radiators are turned off, leaving the heat with nowhere to go.
Turn off the boiler and wait 20 minutes for it to cool down.Ensure all radiator valves and the boiler's isolation valves are fully open.Locate the reset button (often marked with a flame symbol or 'R') and press it once.
Your boiler has tried to start but could not create or detect a flame, causing it to shut down for safety.
Why it happens: This fault occurs when the boiler attempts to ignite but cannot confirm a stable flame is present. It is usually caused by a lack of gas reaching the burner, worn-out spark electrodes, or a buildup of debris on the internal components that prevents the ignition process from completing safely.
Check if your gas supply is active by testing another gas appliance like a hob.Ensure your gas meter has credit if you use a pre-payment meter.Press the reset button (indicated by a flame with a cross through it) for three seconds.
Your boiler has failed to keep the flame lit and has locked itself out for safety.
Why it happens: This fault occurs when the boiler successfully lights but then immediately loses the flame signal, causing it to shut down for safety. The most common reasons are worn-out sensors that can no longer 'see' the flame or a gas valve that isn't providing a steady enough flow of fuel to keep the burner lit.
Check that your gas supply is turned on and other gas appliances are working.If you have a pre-payment meter, ensure you have sufficient credit.Press the Reset button (the flame symbol with a cross) for one second to see if the boiler restarts.
Your boiler has got too hot and stopped working to protect itself, likely because the water isn't moving through the system properly.
Why it happens: This fault occurs when the internal temperature sensors detect that the water inside the boiler has exceeded a safe limit, triggering an emergency shutdown to prevent damage. The most common reason is a failure in the circulation pump or a blockage in the pipework, which stops heat from being carried away from the burner quickly enough. It can also be caused by 'kettling' due to a build-up of limescale or sludge within the main heat exchanger.
Check that all radiator valves are fully openEnsure the boiler pressure is between 1 and 1.5 bar on the gaugePress the 'Reset' button (flame symbol with a cross) to restart the appliance
on the Vaillant ecoMAX Pro 28E
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 Vaillant 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