BoilerFaultCodesThe 6 most common faults
Your boiler has stopped working because the water pressure inside the system is too low to circulate heat safely.
Check the pressure gauge on the front of the boiler; if it is below 1 bar, you need to repressurise the system.Open the filling loop valves (usually a small silver lever or key underneath the boiler) to let water in until the needle reaches 1.5 bar.Close the filling loop valves firmly and bleed your radiators if they feel cold at the top.
Your boiler has lost water pressure, meaning there isn't enough water inside for the pump to circulate properly.
Check the pressure gauge on the front of the boiler; it should be between 1 and 1.5 bar.Locate the filling loop (braided silver hose) underneath the boiler and open the valves to top up the pressure.Bleed your radiators to remove any trapped air, then re-check the pressure gauge.
Your boiler has overheated because the water inside is not moving correctly or has become too hot, causing a safety sensor to shut the system down.
Check the pressure gauge is between 1.0 and 1.5 barBleed all radiators to remove trapped airEnsure at least two radiator valves are fully open to allow water flowReset the boiler using the reset button
Your boiler is failing to light because it cannot detect a flame, meaning your heating and hot water will not work.
Check that your gas meter is turned onIf you have a pre-payment meter, ensure you have creditCheck if other gas appliances, like a cooker, are workingPress the Reset button for five seconds
Your boiler has lost its unique configuration settings, which means the main internal controller cannot read the instructions it needs to operate correctly.
Full guide for Code plug not detected.Your boiler is struggling to push air through its system because the internal fan is not spinning at the required speed, which prevents it from firing up safely.
Full guide for Fan speed too low.on the Worcester Bosch Greenstar 25CDi
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