BoilerFaultCodesThe 6 most common faults
01
L3 High DIY-safe
Your boiler has stopped working because the water pressure inside the system has dropped too low to operate safely.
What to try first
Locate the external filling loop, which is a silver braided hose under the boiler.Open the small black or blue valves on either end of the hose to allow mains water into the system.Watch the pressure gauge on the front of the boiler until the needle reaches the green zone (usually around 1.5 bar).Close both valves tightly to stop the flow of water.
02
L2 High Engineer
Your boiler is trying to start but cannot get the flame to light or stay lit.
Full guide for L203
L1 High Engineer
Your boiler has lost communication with its internal memory chip, meaning it cannot operate safely until the settings are restored or the component is replaced.
Full guide for L104
L4 High Engineer
Your boiler has detected that the flame inside has gone out unexpectedly, so it has shut itself down to keep your home safe.
Full guide for L405
L5 High Engineer
Your boiler has detected that the internal mechanism responsible for safely venting exhaust gases is not working correctly, so it has safely shut itself down to prevent operation.
Full guide for L506
L6 High Engineer
Your boiler has stopped working because a sensor that measures the temperature of the water flowing out to your radiators is not sending a correct signal.
Full guide for L6on the Ideal Independent C24
Filling loopPressure relief valvePressure sensorIgnition electrodeGas valveIgnition lead
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