BoilerFaultCodesThe 6 most common faults
01
204 High Engineer
Your boiler has detected that the water inside the unit is getting hotter than the temperature setting, so it has purposefully turned itself off to prevent overheating.
Why it happens: Temperature control issue
Full guide for 20402
213 High Engineer
Your boiler has detected that the water leaving the boiler is much hotter than the water returning to it, suggesting the system is struggling to circulate heat properly.
Why it happens: Temperature differential fault
Full guide for 21303
214 High Engineer
Your boiler has detected that the internal fan is not spinning as expected during start-up, so it has safely shut down to prevent unsafe operation.
Why it happens: Fan operation fault
Full guide for 21404
223 High Engineer
Your boiler has lost the connection to one of its temperature sensors, meaning it cannot accurately measure how hot the water is and has stopped working as a safety precaution.
Why it happens: Sensor connection fault
Full guide for 22305
224 High Engineer
Your boiler has switched itself off because it has detected an unsafe rise in internal temperature and needs to be inspected by a professional.
Why it happens: Safety mechanism activated
Full guide for 22406
227 High Engineer
Your boiler is attempting to start but is unable to detect a steady flame, so it has safely shut down to prevent gas from escaping.
Why it happens: Ignition failure
Full guide for 227on the Worcester Bosch Greenstar 1000
NTC temperature sensorPrimary heat exchangerCirculating pumpCirculation pumpSystem filterDiverter valve
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
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