BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has become too hot inside and needs time to cool down before it can restart.
Check that all radiator valves are fully open to allow water to flow.Ensure there is enough pressure in the system by checking the gauge.Wait for the unit to cool down and press the reset button located on the control panel.
Your boiler has detected that there is not enough water pressure in the system to operate safely, causing it to shut down to prevent overheating.
Check the pressure gauge on the front of the boiler; it should ideally be between 1 and 1.5 bar.Locate the filling loop (usually a silver flexible hose underneath the boiler).Slowly open the valves to let water into the system until the gauge reaches the green zone, then close them tightly.Press the reset button on the boiler control panel.
Your boiler has stopped working because water is not flowing through the system properly, which is likely caused by a lack of pressure, a pump issue, or a blockage.
Check the pressure gauge on the front of the boiler; if it is below 1.0 bar, top it up to 1.5 bar using the filling loop.Ensure all radiator valves are fully open to allow water to circulate.Gently bleed your radiators to remove any trapped air that might be blocking the flow.
Your boiler is failing to light the gas flame required to provide heating and hot water.
Check if other gas appliances, like a cooker, are working to ensure gas is being supplied to the property.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 one second to attempt a restart.
Your boiler has lost its flame while running and cannot stay lit, meaning your heating and hot water will stop working.
Check if other gas appliances, like a cooker, are working to confirm your gas supply is on.If you have a prepayment meter, check that you have sufficient credit.During very cold weather, check if the white plastic condensate pipe leading outside has frozen and gently thaw it with warm water.Press the reset button (indicated by a flame symbol with a cross) for one second.
Your boiler has failed to ignite, which means it cannot provide the heating or hot water you need.
Check if your gas supply is active (e.g., check other gas appliances or your meter credit)Locate the lockout/reset button on the front panel and press it for 2-3 secondsEnsure the external flue outlet is not obstructed by debris or ice
on the Vaillant Combi Compact 242EB
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