This Fault Code Hub is designed for homeowners, landlords and engineers seeking clear, model-specific explanations of Worcester boiler fault codes. It covers legacy, discontinued and current models, explaining what each code means, why it happens and what action to take next.
Safety note: Reset the boiler only once. Repeated lockouts require the services of a Gas Safe-registered engineer.
Popular models: Greenstar 25i & 30i
Status: Discontinued (replaced by Greenstar 4000)
Description: The Boiler has lost electrical power
Cause: Power cut, blown fuse, loose spur connection
What to do:
• Check mains power and boiler fuse
• Restore power and reset once
• Call an engineer if it keeps recurring
Description: Fan fails to start
Cause: Fan motor fault or wiring issue
What to do:
• Check for visible blockages
• Reset boiler
• Fan replacement required if fault returns
Description: Fan running outside safe limits
Cause: Dirty fan, faulty sensor, PCB issue
What to do:
• Power off and reset
• Engineer to clean or replace the fan
Description: Fan cuts out mid-cycle
Cause: Loose wiring or failing fan
What to do:
• Reset boiler
• Electrical inspection required
Description: The Fan continues running when it should stop
Cause: Control board or relay fault
What to do:
• Switch off the boiler
• PCB replacement is usually required
Description: Incorrect flow temperature reading
Cause: Faulty NTC sensor or wiring
What to do:
• Check connections
• Sensor replacement if error persists
Description: Boiler overheated
Cause: Pump failure, airlock, blocked system
What to do:
• Bleed radiators
• Check pressure
• System flush or pump repair
Description: Burner failed to light
Cause: Gas supply issue, ignition electrode fault
What to do:
• Check gas supply
• Reset once
• Engineer inspection required
Description: Unsafe flame signal
Cause: Gas valve or PCB fault
What to do:
• Do NOT repeatedly reset
• Gas valve replacement required
Description: Flame signal is present incorrectly
Cause: Electrode or gas valve issue
What to do:
• Reset boiler
• Professional repair required
Description: Control box or module error
Cause: Loose wiring, defective HCM or PCB
What to do:
• Power cycle once
• Module replacement is usually required
Description: Pump not circulating water
Cause: Low pressure, airlock, seized pump
What to do:
• Top up pressure
• Bleed system
• Replace pump if needed
Description: Poor circulation detected
Cause: Sludge, blocked heat exchanger, pump issue
What to do:
• System flush
• Check pump and valves
Description: Internal diagnostic modes
Cause: Engineer testing or stuck sequence
What to do:
• Reset boiler
• No fault unless code remains
Description: Heat Control Module or PCB fault
Cause: Incorrect module or internal board failure
What to do:
• Correct module fitting
• PCB replacement if unresolved
Description: Fan speed abnormal or not running
Cause: Fan obstruction or electrical fault
What to do:
• Clear blockage
• Fan replacement
Description: Return temperature sensor issue
Cause: Wet, damaged or disconnected sensor
What to do:
• Dry or replace the sensor
Description: Ignition or flame signal error
Cause: Electrode, ignition lead, gas valve
What to do:
• Reset once
• Engineer diagnosis required
Description: Pump not circulating water
Cause: Leak, low pressure, air in system
What to do:
• Top up pressure
• Bleed system
Description: Hot water temperature is incorrect
Cause: Faulty NTC sensor
What to do:
• Replace sensor
Description: Loss of control signal
Cause: Cable or PCB issue
What to do:
• Check wiring
• Engineer repair
Description: Insufficient airflow
Cause: Fan or flue issue
What to do:
• Fan replacement
Description: Flame or ignition fault
Cause: Gas valve, electrode, PCB
What to do:
• Gas Safe engineer required
Description: Boiler overheated
Cause: Low water pressure or circulation fault
What to do:
• Top up to 1.5 bar
• Press reset
Description: Ignition failed
Cause: Ignition electrode or gas supply issue
What to do:
• Reset once
• Engineer inspection
Description: Flame detected incorrectly
Cause: Ionisation fault
What to do:
• Electrode or valve replacement
Description: Wrong module installed
Cause: Incorrect component
What to do:
• Fit the correct code plug
Description: Advanced sensor, pressure or gas faults
Cause: Multiple internal errors
What to do:
• Full diagnostic required
Description: DHW sensor not reading correctly
Cause: Sensor loose or failed
What to do:
• Refit or replace sensor
Description: Internal software error
Cause: Firmware malfunction
What to do:
• Manufacturer engineer visit required
Description: The Boiler has no power
Cause: Fuse, spur or supply issue
What to do:
• Check power and fuse
Description: Lockout condition
Cause: Fan, sensor or ignition fault
What to do:
• Reset once
• Engineer if repeated
Description: Overheat or ignition lockout
Cause: Circulation or ignition problem
What to do:
• Bleed system
• Engineer inspection
Description: Ignition or gas valve error
Cause: Burner or valve malfunction
What to do:
• Gas Safe repair required
Description: Sensor or control unit faults
Cause: Wiring or board failure
What to do:
• Replace affected components
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