BoilerFaultCodesThe 6 most common faults
Your boiler has shut itself down because it has become too hot to operate safely.
Check that your radiator valves are open and not turned to the lowest settingEnsure there is enough water pressure in the system by checking the gaugeWait 20 minutes for the unit to cool down and then press the Reset button (flame symbol)
Your boiler has stopped working because there is not enough water pressure in the system to operate safely.
Locate the filling loop (usually two braided hoses or blue levers) underneath or near the boiler.Slowly open the valve(s) until you hear water entering the system.Watch the pressure gauge and close the valves tightly once it reaches between 1.0 and 1.5 bar.
Your boiler has shut down because the internal water temperature is rising too quickly or unevenly, usually due to a circulation blockage.
Check that all radiator valves are fully openCheck the boiler pressure gauge and top up to 1.5 bar if lowReset the boiler using the flame/reset button
Your boiler is overheating too quickly because water isn't moving through the system properly, causing it to shut down for safety.
Check that your radiator valves are fully openEnsure your external heating bypass valve is openCheck that the boiler pressure is between 1.0 and 1.5 bar on the gauge
Your boiler has tried to light several times but has been unable to establish a flame, meaning you have no heating or hot water.
Check if your gas meter has credit and the valve is openCheck if other gas appliances like a hob are workingPress the Reset button (the flame symbol) for 3 seconds
Your boiler has lost its flame while it was running and cannot manage to light itself back up.
Check if other gas appliances like a hob are working to ensure gas supply is active.If it is freezing outside, check if the white plastic condensate pipe leading outdoors is frozen and thaw it with warm water.Press the reset button (represented by a flame with a cross through it) for five seconds.
on the Vaillant Home System
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