BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
Locate the external filling loop, which is usually a silver braided hose underneath the boiler.Open the valves at both ends of the hose to allow water into the system until the pressure gauge reads between 1 bar and 1.5 bar.Close both valves firmly and ensure the hose is disconnected if required by your specific installation.
Your boiler is taking longer than it should to light the flame, which is preventing the heating from starting up properly.
Check that your gas emergency control valve is in the 'on' positionIf you have a pre-pay gas meter, check that you have sufficient creditPress the reset button (indicated by a flame symbol with a cross) for three seconds
Your boiler is struggling to light its flame and is failing to stay on regularly, which may leave you without heating or hot water.
Check that your gas meter has credit (if using prepay)Check that other gas appliances in your home are working correctlyEnsure the condensate pipe (outside white plastic pipe) isn't frozen if the weather is very coldReset the boiler using the flame/reset button
Your boiler has encountered a general communication error or internal electronic fault that is preventing it from running properly.
Locate the power switch or fused spur for the boiler.Turn the power off, wait for 30 seconds, and turn it back on.Press the reset button (indicated by a flame with a line through it) on the boiler control panel.
Your boiler has lost its connection to the sensor that measures how hot the water is inside it, preventing it from heating your home safely.
Full guide for F.00Your boiler has lost its connection to the sensor that monitors the water temperature returning to the unit, causing it to shut down for safety reasons.
Full guide for F.01on the Vaillant ecoFIT Pure 425
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