BoilerFaultCodesThe 6 most common faults
Your boiler has stopped running for safety reasons and needs to be manually restarted to try and get your heating and hot water back on.
Why it happens: This fault occurs when the boiler attempts to light the burner but fails to detect a stable flame. The most common reasons include a lack of gas reaching the unit, worn-out spark components that cannot ignite the fuel, or a sensor that is too dirty to recognize that a flame is actually present.
Locate the reset button on the front control panel.Press and hold the reset button for at least one second.Wait for the boiler to restart; if the light stops flashing, the boiler should resume normal operation.
Your boiler has detected a general internal fault and has locked itself out to prevent damage.
Why it happens: This fault occurs when the boiler's internal computer identifies a communication failure between vital components, most often involving the fan or the air pressure switch. It acts as a safety shutdown because the system cannot confirm that harmful exhaust gases are being safely vented outside. Over time, electrical wear on the main control board or a buildup of debris in the fan can trigger this sudden stop.
Turn the main power switch to the boiler offWait for 30 secondsTurn the power back on to see if the fault clears
Your boiler has stopped working because it cannot light the gas needed to create heat, often due to an ignition or sensor failure.
Why it happens: This fault occurs when the boiler attempts to ignite but fails to detect a steady flame after several tries. The most common reasons are worn-out ignition sparks that can no longer light the gas or a layer of carbon buildup on the sensor that prevents the boiler from 'seeing' the flame even if it is actually lit.
Full guide for Burner LockdownYour boiler's internal computer brain is failing to communicate correctly, often due to moisture or a significant electronic fault.
Why it happens: This fault occurs when the boiler's main control board suffers a critical internal failure or a loss of signal between components. The most common reason is moisture ingress from a small internal leak or dampness in the air reaching the electronics and short-circuiting the board. In some cases, it can also be triggered by a loose or damaged wiring harness that prevents the boiler's 'brain' from sending instructions to the rest of the unit.
Full guide for Condition KYour boiler has detected dangerous exhaust fumes leaking back into the unit, which is a serious safety risk and has caused the system to shut down.
Why it happens: This fault occurs when the boiler's internal sensors detect that poisonous exhaust gases are leaking back into the casing instead of being safely expelled outside. The most common reasons are a blockage in the flue pipe, a cracked internal seal, or heavy debris buildup within the heat exchanger that prevents the fumes from flowing away correctly.
Full guide for Flue Spillage FaultYour boiler is struggling to light its small internal pilot flame, which means it cannot fire up to provide heating or hot water.
Check if your gas meter is turned on or has creditCheck if other gas appliances, like a cooker hob, are workingTry resetting the boiler using the reset button or dial
on the Worcester Bosch 24CDi BF
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