BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because it has detected that the internal temperature has become too hot and reached a dangerous level.
Why it happens: This fault occurs when the water inside the boiler gets too hot too quickly, triggering a safety sensor to shut the system down to prevent damage. The most common reasons are a pump failure that stops water from moving or a blockage in the heat exchanger that traps heat inside the unit.
Check that all radiator valves are fully open to allow water to flow.Ensure there is enough water pressure in the system (typically 1.0 to 1.5 bar).Press the reset button (flame symbol with a cross) once to see if the fault clears.
Your boiler has detected that there is not enough water pressure inside the system to operate safely, causing it to shut down to prevent overheating.
Why it happens: This fault occurs when the boiler's internal sensors detect a lack of water, meaning there isn't enough pressure to safely transfer heat away from the burner. The most common reason is a slow leak somewhere in your radiator system or a component inside the boiler, such as the air vent, letting water escape over time.
Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.Locate the external filling loop (usually a silver flexible hose) under or near the boiler.Slowly open both valves on the loop until you hear water entering and the gauge reaches 1.5 bar, then close them tightly.Press the reset button (indicated by a flame with a line through it) to restart the boiler.
Your boiler has stopped working because the water isn't circulating properly between the pipes, causing a sudden and unsafe temperature gap.
Why it happens: This fault occurs when the water inside your boiler heats up too quickly because it isn't moving around the system fast enough. The most common reason is a failing pump that can no longer push the water through the pipes, or a blockage in the heat exchanger that is restricting flow. When the boiler detects such a large temperature difference between the water going out and the water coming back, it shuts down to prevent internal damage.
Check that the boiler pressure is between 1.0 and 1.5 bar on the gaugeEnsure all radiator valves and isolation valves under the boiler are fully openTry bleeding your radiators to remove any trapped air pocketsReset the boiler to see if the fault clears
Your boiler is heating up much too fast because there isn't enough water moving through the system to carry the heat away.
Why it happens: This fault occurs when the heat inside the boiler builds up much faster than the water can carry it away to your radiators. The most common reasons are a pump that has failed or become stuck, a significant blockage of sludge in the pipework, or air trapped within the system. Essentially, the boiler is forced to shut down to prevent itself from overheating.
Check the pressure gauge and top up the water to between 1 and 1.5 bar using the filling loopEnsure all radiator valves and isolation valves under the boiler are fully openBleed your radiators to remove any trapped air pockets
Your boiler has tried to light several times but has been unable to establish a flame, meaning you have no heating or hot water.
Why it happens: This fault occurs when the boiler attempts to ignite but cannot confirm that a steady flame has been established. The most common reasons include a lack of gas reaching the burner, a worn-out ignition spark, or a buildup of carbon on the sensor that detects the heat.
Check if other gas appliances, like a cooker hob, are working to ensure gas is reaching the property.If you have a prepayment meter, check that you have sufficient credit.Press the Reset button (indicated by a flame with a cross through it) for one second to see if the boiler restarts.
Your boiler was working but the flame has unexpectedly gone out, causing the system to shut down for safety.
Why it happens: This fault happens when your boiler successfully starts up but the flame unexpectedly goes out while it is running. It is usually caused by an interruption in the gas supply, a build-up of carbon on the sensing electrodes, or a blockage in the pipe that carries away waste liquids. When the boiler's internal sensors stop detecting a flame, the system shuts down as a safety precaution.
Check if other gas appliances like your hob are working to ensure gas is reaching the propertyCheck your prehistoric or smart gas meter to ensure you haven't run out of creditPress the reset button (represented by a flame with a line through it) for one second to see if the boiler restarts
on the Vaillant ecoMAX
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