BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
Locate the external filling loop, which is usually a small metal braided hose underneath the boiler.Open the valves on the filling loop to allow cold mains water to enter the system until the pressure gauge reads between 1.0 and 1.5 bar.Close both valves tightly and ensure the filling loop is disconnected if it is a detachable type.
Your boiler has stopped working because the water pressure inside the heating system has dropped too low.
Locate the external filling loop, usually a silver flexible hose with one or two valves underneath the boiler.Open the valve(s) slowly to allow water into the system while watching the pressure gauge on the front display.Stop filling once the needle reaches the green zone, ideally around 1.5 bar, and ensure the valve is fully closed.
Your boiler is signalling that the water pressure is either too low or the sensor monitoring the flow is not detecting any movement, which usually prevents the unit from starting.
Check the system pressure gauge on the front panel; it should be between 1.0 and 1.5 bar.If below 1.0 bar, locate the filling loop lever or tap underneath the boiler.Slowly open the valve to let water in until the needle reaches 1.5 bar, then securely close the valve.
Your boiler has temporarily stopped because it has detected that the water pressure is too low to circulate heat safely.
Locate the external filling loop or internal filling key under the boilerSlowly open the valve to allow water into the systemWatch the pressure gauge on the front of the display until it reaches 1.5 bar, then securely close the valve
Your boiler has lost the signal from the sensor that monitors how hot the water is, meaning it has safely shut itself down to prevent overheating.
Full guide for F.00Your boiler has lost the signal from one of its internal heat sensors, meaning it cannot accurately monitor the temperature of the water returning to the system and has shut down as a precaution.
Full guide for F.01on the Vaillant ecoTEC plus 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