BoilerFaultCodesThe 6 most common faults
Your boiler has detected that there isn't enough water circulating through the system, which is preventing it from heating up safely.
Check the pressure gauge on the front of the boiler; if it is below 1 bar, it needs topping up.Locate the internal or external filling loop and carefully add water until the gauge reads between 1 and 1.5 bar.Bleed any trapped air from your radiators using a radiator key.Reset the boiler to clear the fault code.
Your boiler has shut down because it has detected that the water inside is getting too hot, triggering a safety cut-out to prevent damage.
Check that your radiator valves are open and not turned to zero.Check the boiler pressure gauge and top up to 1.5 bar if it is low.Press the reset button to see if the fault clears once the system has cooled down.
Your boiler is failing to light the gas, which means your heating and hot water will not work until the issue is resolved.
Check if other gas appliances in your home, like a hob, are working to confirm your gas supply is onEnsure your prepaid gas meter has enough creditPress the reset button on the boiler for five seconds
Your boiler's internal computer chip is missing or has lost its connection, meaning the system cannot identify which model it is and has stopped working for safety.
Full guide for 4 flashesYour boiler has stopped working because the fan that helps remove waste gases is not spinning at the correct speed.
Full guide for 5 flashesYour boiler's temperature sensor has failed, meaning the system can no longer monitor how hot the water is and has shut down as a safety precaution.
Full guide for 6 flasheson the Worcester Bosch Greenstar 42CDi
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