BoilerFaultCodesThe 6 most common faults
Your boiler has switched itself off because the water pressure has dropped too low to operate safely.
Why it happens: This fault occurs when the water pressure inside your heating system drops below a safe working level, causing the boiler to shut down to prevent internal damage. The most common reason is a slow leak from a radiator valve or pipework, though it can also happen if you have recently bled your radiators and haven't topped the pressure back up.
Locate the filling loop (usually two silver braided hoses) underneath the boilerSlowly open both taps on the filling loop until you hear water movingClose both taps tightly once the pressure gauge on the screen reaches 1.5 bar
Your boiler has shut itself down because it has detected that it is getting far too hot, usually due to a lack of water flow or a circulation blockage.
Why it happens: This fault occurs when the boiler's internal water temperature rises too quickly or exceeds a safe limit, triggering an emergency shutdown to prevent damage. The most common reasons are a seized pump failing to move water, a buildup of sludge blocking the heat exchanger, or air trapped within the system preventing proper circulation.
Check that your boiler pressure is between 1.0 and 1.5 bar on the digital display or gauge.Ensure all radiator valves are fully open to allow water to circulate.Try resetting the boiler by pressing the button with the flame symbol 'X' crossed out.
Your boiler has shut down because water isn't moving through the system quickly enough, causing it to overheat too rapidly.
Why it happens: This fault occurs when the boiler's internal sensors detect that water is heating up too quickly or that there is a massive temperature difference between the pipes going out and coming back. The most common reason is a blockage or a failing pump preventing the water from circulating through your radiators. It essentially means the heat being generated has nowhere to go, so the boiler shuts down to prevent internal damage from overheating.
Check that all radiator valves (TRVs) are turned to the highest settingEnsure the boiler pressure is between 1.0 and 1.5 bar on the digital displayCheck for recent air locks and bleed your radiators if they have cold spots
Your boiler has shut down because it has detected an issue with a safety sensor or the pump that removes excess water from the system.
Why it happens: This fault occurs when a safety device detects that water isn't draining away correctly or the system is getting too hot. The most common reason is a blockage in the waste water pipe or a failure in the external pump that pushes excess fluid out of the boiler. To prevent internal damage or a leak, the boiler automatically shuts down as a protective measure.
Check if the condensate pump is plugged in and switched onInspect the discharge pipe outside for blockages or freezing during cold weatherGently clear any visible debris from the pump filter if accessible
Your boiler has detected that there is too much water in the system, causing the internal pressure to rise above safe operating levels.
Why it happens: This fault occurs when the water pressure inside your heating system exceeds the safe limit, often because the filling loop used to top up the system has been left slightly open or is leaking. It can also happen if the expansion vessel, which manages heat-related pressure changes, has failed or if the system has been significantly overfilled during recent maintenance.
Check that the filling loop valves are fully closed and not leaking water into the systemBleed water from a radiator using a bleed key to reduce the system pressureMonitor the pressure gauge until it returns to the normal range (typically 1.0 to 1.5 bar)Restart the boiler to clear the status code
Your boiler has temporarily paused because water is not moving through the system fast enough to take the heat away safely.
Why it happens: This fault occurs when the boiler's internal sensors detect that the heat is and building up too quickly because the water isn't flowing away fast enough. The most common reason is a blockage in the system or a failing pump that is struggling to push the water around your radiators. It can also be triggered if there is too much air trapped in the pipework or if your heating valves are bumped shut.
Check that the boiler pressure gauge is between 1 and 1.5 barEnsure all radiator valves and the local bypass valve are fully openCheck for any trapped air in the radiators and bleed them if necessary
on the Vaillant ecoTEC Pro
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
Avoid the next call-out bill
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