BoilerFaultCodesThe 6 most common faults
Your boiler has detected an internal sensor failure and has stopped working to prevent damage or overheating.
Why it happens: This fault occurs when the boiler's internal sensors, which monitor water temperature, stop sending a reliable signal to the main control board. The most common reason is that the sensor has physically degraded or developed an electrical short, meaning the boiler can no longer safely regulate its heat output. In some cases, old or damaged wiring between the sensor and the brain of the boiler is the culprit.
Full guide for Flashing mains LEDYour boiler has detected a problem with one of its internal temperature sensors and has stopped working as a safety precaution.
Why it happens: This fault occurs when the internal temperature sensors, which monitor how hot the water is getting, fail to send a reliable signal to the boiler's brain. The most common reason is that the sensor has physically degraded or developed a chemical build-up over time, causing it to provide inaccurate readings. In some cases, the electrical wiring connecting these sensors has become loose or damaged, leading the boiler to shut down to prevent overheating.
Full guide for INDICATOR LIGHT FLASHINGYour boiler has completely lost power and is unable to turn on, likely due to a blown fuse or a failure in the electrical control board.
Full guide for No mains LEDYour boiler has detected that it got too hot and has automatically shut itself down to prevent damage or fire risk.
Full guide for OVERHEAT CUT-OFFYour boiler has failed to start up or stay burning, so it has purposefully shut itself off to prevent gas from building up.
Full guide for IGNITION LOCKOUTYour boiler has detected an issue with the internal fan or the way it clears exhaust gases, so it has shut down to keep you safe.
Full guide for AIR FLOW DEVICEon the Worcester Bosch 24i RSF
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 Worcester Bosch 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