BoilerFaultCodesThe 6 most common faults
Your boiler is struggling to circulate water because there isn't enough pressure or there is air trapped in the system.
Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.If the pressure is too low, use the filling link underneath the boiler to top it up.Bleed your radiators to remove any trapped air that might be blocking water flow.Reset the boiler by holding the reset button for 3 to 5 seconds.
Your boiler has sensed that the water inside is getting too hot and has shut itself down to prevent overheating.
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 front gaugeReset the boiler by holding the reset button for five seconds
Your boiler has tried to start but could not detect a flame, meaning it cannot heat your water or radiators and has shut down for safety.
Check if other gas appliances in your home (like a hob) are working to ensure gas is reaching the propertyCheck that your gas meter has credit if you have a pre-payment meterIn freezing weather, check if your external condensate pipe is frozen and thaw it with warm waterPress and hold the 'Reset' button for five seconds
Your boiler has sensed that it is getting too hot and has automatically shut down for safety.
Check that your system pressure is between 1 and 1.5 bar on the pressure gaugeOpen all radiator valves fully to ensure water can move freelyPress and hold the 'Reset' button for five seconds
Your boiler is failing to light the gas flame or cannot detect that a flame is present, causing the system to shut down for safety.
Check if your gas supply is active by testing other gas appliances like a hobEnsure your gas meter has credit if you use a pre-payment meterPress and hold the 'Reset' button for five seconds to see if the system clears the fault
Your boiler has lost its memory chip, which tells it exactly how to operate safely, and it has stopped working as a safety precaution.
Full guide for 4 flasheson the Worcester Bosch Greenstar 35 CDi
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