BoilerFaultCodesThe 5 most common faults
Your boiler has detected a safety-related issue and has locked itself out to prevent further damage, requiring a manual reset to restart.
Why it happens: This fault occurs when the boiler fails to detect a stable flame after several attempts to light. The most common reasons include a lack of gas supply, worn-out ignition parts that can no longer create a spark, or a sensor that is too dirty to 'see' the flame even when it is present.
Locate the reset button on the front control panelPress and hold the reset button for at least one secondRelease the button and wait for the boiler to attempt to restartIf the boiler refires, monitor it closely; if the light returns, call an engineer
Your boiler has detected a general internal fault that requires a system reset or power cycle to clear.
Why it happens: This fault occurs when the boiler's internal computer experiences a communication error or fails to complete its safety checking sequence during startup. The most common reason is an electronic glitch within the main control board or a failure in the ignition process that prevents the burner from firing safely. It effectively means the boiler has reached a 'deadlock' where it requires a manual intervention to confirm the system is safe to try again.
Locate the main power switch for the boiler (usually a fused spur nearby) and turn it off.Wait for approximately 30 seconds.Turn the power back on and check if the flashing light stays off and the boiler fires up.
Your boiler has failed to ignite properly, meaning it cannot create the flame needed to heat your home or water.
Why it happens: This fault occurs when the boiler attempts to start but cannot detect a stable flame after several tries. It is usually caused by a lack of gas reaching the burner or a failure in the sparking system that triggers the ignition. In some cases, a faulty internal sensor may simply fail to recognize that the flame is actually lit, leading to a safety shutdown.
Full guide for 2 lights flashing fastYour boiler's main internal computer has developed a serious communication error and cannot operate, often because it has been exposed to water or has suffered an electrical failure.
Why it happens: This fault occurs when the boiler's main control board suffers a critical internal failure and can no longer process data to operate the system. The most common cause is water ingress from a leaking internal component dripping onto the electronics, or a power surge that has damaged the sensitive electrical tracks on the board.
Full guide for FAIL POINT KYour boiler has stopped working because it cannot detect a flame, likely due to a gas supply interruption.
Check that your gas emergency control valve is in the 'on' positionIf you have a pre-payment meter, ensure you have credit and the meter is activeTry resetting the boiler by holding the 'Reset' button for five seconds
on the Worcester Bosch Greenstar Si
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