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 stopped working because it cannot light the flame or keep it burning properly.
Why it happens: This fault occurs when the boiler's control system attempts to light the burner but fails to detect a stable flame after several attempts. The most common reasons are worn-out ignition components that can't create a spark or a faulty sensor that fails to tell the boiler the flame is actually lit.
Check if your gas credit has run out or if other gas appliances in your home are workingPress and hold the reset button (the flame symbol with a cross) for 5 secondsWait 15 minutes and try resetting a second time if it fails again
Your boiler has stopped working because the water pressure is too low for it to operate safely.
Why it happens: This fault occurs when the internal sensors detect that the water pressure has dropped below the minimum level required to protect the heat exchanger from overheating. The most common reason is a slow leak somewhere in your radiator network or a problem with the expansion vessel which helps manage pressure changes. In some cases, it may simply be that you have recently bled your radiators and haven't topped up the system water afterwards.
Locate the silver braided filling loop hoses underneath or near your boilerSlowly open the one or two small taps on the filling loop to allow water into the systemMonitor the pressure gauge until it reaches between 1.0 and 1.5 bar, then close the taps tightly
Your boiler has detected that water isn't moving through the internal pipes correctly, causing it to shut down to prevent overheating.
Why it happens: This fault occurs when the boiler's internal sensors detect a massive temperature difference between the water entering and leaving the unit, usually because the water has stopped moving. The most common reason is a failed internal pump or a heavy buildup of sludge and debris blocking the main heat exchanger. Without proper flow, the water inside the unit reaches a boiling point almost instantly, forcing the system to shut down for safety.
Check that all radiator valves are fully openEnsure the internal boiler valves underneath the unit are in the open positionCheck if the pump is making a humming sound, which may indicate it is stuck
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