BoilerFaultCodesThe 6 most common faults
01
1017 High DIY-safe
Your boiler has lost the water pressure needed to operate and needs to be topped up to work again.
What to try first
Locate the filling link (metal braided hose or plastic key) underneath your boiler.Open the valves slowly to allow water into the system until the gauge reads between 1.0 and 1.5 bar.Close the valves firmly and check for any dripping water.
02
2971 B High DIY-safe
Your boiler has stopped working because the water pressure inside the heating system has dropped too low to operate safely.
What to try first
Locate the external filling loop or internal key under the boilerSlowly open the valve to let water into the system while watching the pressure gaugeClose the valve tightly once the needle reaches the green zone, typically between 1.0 and 1.5 bar
03
214 High Engineer
Your boiler has detected that the internal exhaust fan has failed to start or stopped unexpectedly, so it has safely turned itself off to prevent a buildup of fumes.
Full guide for 21404
224 High Engineer
Your boiler has detected that it is running dangerously hot and has shut itself down to prevent internal damage.
Full guide for 22405
227 High Engineer
Your boiler is trying to start but the flame is failing to light or stay lit, so it has safely shut itself down to prevent a gas build-up.
Full guide for 22706
233 High Engineer
Your boiler has lost the ability to communicate with its internal control system, meaning it has safely shut itself down to prevent operational errors.
Full guide for 233on the Worcester Bosch Greenstar 4000
Filling loopPressure relief valveExpansion vesselFan assemblyWiring harnessPrinted Circuit Board (PCB)
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