BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
Locate the external filling loop, which is usually a flexible silver braided hose under your boiler.Open the valves at both ends of the hose to let mains water into the system until the pressure gauge reads between 1 and 1.5 bar.Close both valves tightly to stop the flow of water and check the gauge remains steady.
Your boiler has stopped heating your radiators and water because the internal water pressure has dropped too low.
Locate the filling loop (usually a silver braided hose with one or two valves) underneath the boiler.Slowly open the valve(s) to let water enter the system while watching the pressure gauge on the front panel.Stop when the needle reaches the green zone, ideally around 1.5 bar, and ensure the valve is tightly closed.
Your boiler has switched itself off for safety and is displaying a 'lockout' status, which will be accompanied by a second flashing code to tell you exactly what is wrong.
Check the display for the secondary flashing number or letter that follows the 'L'Press and hold the 'Reset' button for two secondsCheck if your gas credit has run out or if other gas appliances are working
Your boiler has stopped working because it has detected a specific internal problem, which it will show by alternating the 'F' with another number or letter.
Wait for the display to flash the number or letter following the 'F' to identify the specific fault.Try resetting the boiler by turning the mode knob to 'Reset' for two seconds and then back to the original setting.Check that your gas supply is active and your prepaid meter (if applicable) has credit.
Your boiler has shut down because it has reached an unsafe temperature, essentially tripping a safety switch to prevent damage.
Check that all radiator valves are fully open to allow water to circulateEnsure the system pressure is between 1 and 1.5 bar on the pressure gaugePress the reset button and wait for the temperature to drop below 50°C for the boiler to restart
Your boiler has failed to light the flame or keep it running, so it has safely shut itself off to prevent gas build-up.
Full guide for L Fon the Ideal Isar 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 Ideal 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