Worcester Bosch Boiler Fault Codes
Greenstar combi, system and heat-only boilers. Older models show letter codes (EA, C6, A1); newer Greenstar 8000, 4000 and Lifestyle models show numeric codes on the display.
Applies to: Greenstar i, CDi Classic, Greenstar 2000 / 4000 / 8000, Greenstar Lifestyle
Worcester Bosch 227
No flame detected
The numeric-display equivalent of an ignition fault — the boiler cannot detect a flame.
Worcester Bosch 1017
Low water pressure
System pressure has dropped too low for the boiler to run safely.
Worcester Bosch A1
Pump / circulation fault (dry fire protection)
The boiler is not sensing proper water circulation, so it has shut down to protect itself.
Worcester Bosch C6
Fan fault
The fan is not running at the speed the boiler expects, so it will not light for safety.
Worcester Bosch D5
PCB / internal communication fault
The control board has detected an internal fault or a communication problem.
Worcester Bosch E9
Overheat — primary temperature too high
The boiler has sensed the primary water getting too hot and shut down on the overheat thermostat.
Worcester Bosch EA
Ignition / flame detection lockout
The boiler tried to light but did not detect a flame, so it has locked out for safety.
Worcester Bosch F0
Internal / sensor fault
A general internal fault, usually a temperature sensor reading out of range or a wiring fault.
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