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 (a flexible silver hose connecting two pipes near the boiler).Open the valves at both ends of the hose to let mains water into the system.Monitor the boiler's pressure gauge until the needle reaches the green zone (typically 1.0 to 1.5 bar).Close both valves tightly and remove the filling loop if required by your specific model.
Your boiler has stopped working because the amount of water inside your heating system has dropped too low to operate safely.
Locate the external filling loop, which is a flexible 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 and 1.5 bar.Ensure both valves are tightly closed and check for any visible leaks on your radiators or pipework.
Your boiler is trying to start up but cannot successfully light the internal flame to provide heat or hot water.
Full guide for A01Your boiler has detected that it is running too hot and has automatically turned itself off to prevent damage.
Full guide for A03Your boiler has detected multiple issues with its internal temperature sensing or airflow, causing it to lock itself down for safety.
Full guide for A04Your boiler has stopped working because it cannot detect if the fan, which is essential for safely venting exhaust gases, is spinning correctly.
Full guide for A05on the Ferroli Optimax HE Plus
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 Ferroli 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