BoilerFaultCodesThe 6 most common faults
01
A7 High Engineer
Your boiler is currently struggling to measure the temperature of the water it is heating, which means it will stop providing you with hot water.
Full guide for A702
B1 High Engineer
Your boiler's internal computer is struggling to identify the specific settings it needs to operate, so it has safely shut down to prevent incorrect functioning.
Full guide for B103
C6 High Engineer
Your boiler has detected that the internal fan responsible for clearing exhaust gases is not spinning at the correct speed to operate safely.
Full guide for C604
d1 High Engineer
Your boiler is struggling to accurately measure its own temperature, so it has safely shut itself down to prevent potential damage.
Full guide for d105
E2 High Engineer
Your boiler has lost the ability to measure the temperature of the water used for your radiators, so it has safely shut down to prevent overheating.
Full guide for E206
E9 High Engineer
Your boiler has detected that it is running too hot and has automatically shut itself down to prevent damage.
Full guide for E9on the Worcester Bosch Greenstar 30si
Domestic Hot Water NTC SensorCoding plugPrinted Circuit Board (PCB)Fan assemblyWiring harnessNTC Temperature Sensor
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