BoilerFaultCodesThe 6 most common faults
Your boiler has become too hot and has shut itself down as a safety precaution to prevent damage.
Switch the boiler off and allow it to cool for 20 minutesCheck that all radiator valves are fully open to allow water to flowPress the reset button (flame symbol with a cross) to restart the system
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.
Locate the filling loop (usually two silver braided hoses with small valves) underneath the boiler.Slowly open both valves until you hear water flowing and the pressure gauge reaches between 1.0 and 1.5 bar.Close both valves tightly and press the reset button on the boiler control panel.
Your boiler is struggling to move water through the system, which is causing it to stop running to prevent overheating.
Check if the pressure gauge is between 1 and 1.5 bar and top up if lowEnsure all radiator valves are fully open to allow water flowBleed your radiators to remove any trapped air pockets
Your boiler is failing to light because it isn't getting enough gas or the spark that starts the flame is not working correctly.
Check if your gas meter has credit (if on a prepayment meter)Check if other gas appliances, like a cooker, are working to confirm gas supplyReset the boiler by pressing the flame symbol button for 3 seconds
Your boiler has lost its flame while running and cannot stay lit, meaning your heating and hot water have stopped.
Check if other gas appliances, like a hob, are working to confirm gas supply.If you have a prepayment meter, ensure it has sufficient credit.Press the 'Reset' button (flame symbol with a cross) on the control panel once.
Your boiler's internal control board has become too hot to operate safely and has shut down to protect itself.
Turn off the boiler at the main power switch.Wait for 30 minutes to allow the electronic components to cool down naturally.Ensure there is adequate ventilation around the boiler casing and switch it back on.
on the Vaillant Atmomax
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