BoilerFaultCodesThe 6 most common faults
01
EA High DIY-safe
Your boiler has tried to light several times but has been unable to detect a flame, causing the system to shut down for safety.
What to try first
Check if your gas supply is active by testing other gas appliances like a hobEnsure your gas meter has credit if you use a pre-payment meterPress and hold the 'Reset' button for five seconds to see if the boiler restartsCheck that the condensate pipe (outside white plastic pipe) isn't frozen if the weather is very cold
02
F0 High Engineer
Your boiler has temporarily stopped working because it cannot properly read its internal temperature sensors.
Full guide for F003
C7 High Engineer
Your boiler has stopped working because the internal component responsible for pushing air through the system is failing to start.
Full guide for C704
C6 High Engineer
Your boiler's internal fan is spinning faster than it should, which has caused the system to shut down for safety.
Full guide for C605
E5 High Engineer
Your boiler has detected that the water inside the system is getting much hotter than it should be, so it has shut itself down to prevent damage.
Full guide for E506
E9 High Engineer
Your boiler has temporarily shut down because the internal safety sensor detected that the water temperature has risen too high.
Full guide for E9on the Worcester Bosch Greenstar 25 Si Compact
Ignition ElectrodeFlame Sensor (Ionisation Probe)Gas ValvePrinted Circuit Board (PCB)NTC ThermistorInternal Wiring Harness
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