Worcester Bosch boiler fault codes
Detailed Guide of Worcester Boiler Fault Codes
In this guide, we explain the most common and legacy Worcester Bosch fault codes, what they mean, what you can safely do yourself, and when to call a Gas Safe registered engineer. We can diagnose and fix error codes, ensuring your boiler runs safely and efficiently.
Whether you have a modern Greenstar model or an older boiler, this guide will help you understand the codes and troubleshoot issues while keeping your warranty valid.
Ignition & Flame Issues - Worcester Boiler Fault Codes
Typical Cause:
Boiler cannot ignite. Often caused by gas supply issues, faulty electrodes, blocked condensate, or flame detection faults.
What to do:
- Check gas supply.
- Reset once.
- Check for frozen condensate pipe.
Call an engineer if:
- The error repeats.
- Ignition electrodes or gas valve need testing.
Typical Cause:
Overheating caused by poor circulation or faulty temperature sensors.
What to do:
- Check system pressure.
- Bleed radiators.
Call an engineer if:
- Overheating continues.
- Faulty thermostat or NTC sensor suspected.
Typical Cause:
Condensate blockage or freezing causes incorrect flame readings.
What to do:
- Check outside condensate pipe.
- Thaw if frozen.
Call an engineer if:
- Internal blockage remains.
- Flame sensor faults persist.
Typical Cause:
The boiler thinks the outgoing water temperature is too high or the sensor can’t read correctly. This could mean a faulty flow thermistor, limescale buildup restricting water flow, or poor circulation due to a weak pump.
What to do:
- Check that radiator valves are open and the system is not blocked.
- Ensure the boiler has not overheated recently.
Call an engineer if:
- The fault continues after system checks.
- Thermistors (temperature sensors) may need replacing.
Typical Cause:
Flame not recognised despite ignition. Can be caused by dirty or wet flame sensor, faulty wiring, or PCB issues.
What to do:
- Reset the boiler once.
- Check for moisture on flame sensor.
Call an engineer if:
- Flame sensor or wiring is faulty.
- PCB malfunction suspected.
Typical Cause:
Boiler failed to ignite after several attempts.
What to do:
- Press the reset button once.
Call an engineer if:
- Repeated lockouts occur.
Typical Cause:
Flame detected incorrectly or unstable flame.
What to do:
- Press reset once.
Call an engineer if:
- Gas valve or PCB faults are present.
Low Pressure & Circulation Issues - Worcester Boiler Fault Codes
Typical Cause:
Poor circulation, low system pressure, or airlock causes boiler to overheat.
What to do:
- Check system pressure (1.0–1.5 bar cold).
- Bleed radiators.
- Reset the boiler once.
Call an engineer if:
- Pressure keeps dropping.
- Pump is noisy or blocked.
Typical Cause:
Not enough water for pump to circulate. Often low pressure or trapped air.
What to do:
- Repressurise the boiler.
- Bleed radiators.
Call an engineer if:
- Pump continues running dry.
Typical Cause:
System pressure below minimum operating level, usually due to leaks or bleeding radiators.
What to do:
- Check pressure gauge (~1–1.5 bar cold).
- Repressurise using filling loop if safe.
- Inspect for leaks.
Call an engineer if:
- Pressure keeps dropping.
- Leaks persist.
Typical Cause:
Poor circulation, blocked radiators, pump failure, or faulty flow temperature sensor.
What to do:
- Bleed radiators.
- Ensure valves open.
- Check pressure and reset boiler.
Call an engineer if:
- Fault persists after circulation is corrected.
- Sensor or pump may be faulty.
Typical Cause:
Low flow rate detected in the system. Usually blocked radiators, pump issues, or pipework restriction.
What to do:
- Open all radiator valves.
- Check pressure.
- Reset boiler once.
Call an engineer if:
- Fault persists.
- Pump, sensor, or blockage needs professional inspection.
Typical Cause:
Pump failure or severe airlock in the system.
What to do:
- Bleed radiators.
- Check pump for operation.
- Reset boiler once.
Call an engineer if:
- Pump replacement required.
Typical Cause:
Flow temperature detected as too high—often blocked valves, pump failure, or limescale buildup.
What to do:
- Open all radiator valves.
- Check circulation and pressure.
- Reset boiler once.
Call an engineer if:
- Flow continues to overheat.
- Pump or thermostat needs professional inspection.
Sensor & Temperature Issues - Worcester Boiler Fault Codes
Typical Cause:
The flow temperature sensor (NTC) is faulty, misreading, or has a loose connection.
What to do:
- Reset the boiler once.
- Check that system pressure is correct.
- Ensure radiators and valves are open for circulation.
Call an engineer if:
- Sensor or wiring is damaged.
- Flow temperatures remain inconsistent.
Typical Cause:
The return temperature sensor (NTC) is faulty, misreading, or has loose connections.
What to do:
- Reset the boiler once.
- Ensure radiators are open and circulating.
- Check system pressure.
Call an engineer if:
- Sensor replacement is needed.
- Circulation issues persist.
Typical Cause:
The flow temperature is detected as too high due to restricted circulation, closed radiator valves, pump issues, or limescale buildup.
What to do:
- Check that all radiator valves are open.
- Ensure pump is working properly.
- Check system pressure.
- Reset boiler once.
Call an engineer if:
- Overheating continues despite circulation correction.
- Pump, thermostat, or NTC sensor requires replacement.
Typical Cause:
The hot water temperature sensor is faulty or misreading, causing no hot water or incorrect temperatures.
What to do:
- Reset the boiler once.
- Check system pressure.
- Ensure correct circulation.
Call an engineer if:
- Thermistor replacement is required.
- Hot water remains inconsistent or does not heat.
Typical Cause:
Return sensor misreading due to faulty NTC, wiring, or circulation issues.
What to do:
- Check radiator valves are open.
- Bleed radiators if necessary.
- Reset boiler once.
Call an engineer if:
- Sensor replacement required.
- Wiring or pump issues suspected.
Typical Cause:
Flow sensor misreading due to faulty NTC, wiring, or circulation issues.
What to do:
- Check radiator valves and pressure.
- Reset boiler once.
Call an engineer if:
- Flow sensor replacement is needed.
- Internal wiring faults suspected.
Fan & Airflow Issues - Worcester Boiler Fault Codes
Typical Cause:
The boiler fan is not spinning at the correct speed, affecting safe combustion.
What to do:
- Reset boiler once.
- Check the condensate pipe for blockages (can affect airflow).
Call an engineer if:
- Fan motor is sticking or burnt out.
- PCB or wiring faults are present.
Typical Cause:
Pressure switch not detecting airflow due to blockage or fan issue.
What to do:
- Check for blockages in the flue.
- Reset boiler once.
Call an engineer if:
- APS or fan motor replacement needed.
- PCB or wiring faults persist.
Condensate & Moisture Issues - Worcester Boiler Fault Codes
Typical Cause:
Moisture detected around sensors or electrical components, usually caused by blocked or frozen condensate pipe or internal water ingress.
What to do:
- Check and clear condensate pipe externally.
- Ensure pipe has continuous downhill run to drain.
- Dry any visible moisture (power off).
- Reset boiler once.
Call an engineer if:
- Fault returns after clearing pipe and drying sensors.
- Internal condensate traps are blocked.
- PCB or sensors are damaged by water ingress.
Typical Cause:
Moisture detected around sensors or electrical components, usually caused by blocked or frozen condensate pipe or internal water ingress.
What to do:
- Check and clear condensate pipe externally.
- Ensure pipe has continuous downhill run to drain.
- Dry any visible moisture (power off).
- Reset boiler once.
Call an engineer if:
- Fault returns after clearing pipe and drying sensors.
- Internal condensate traps are blocked.
- PCB or sensors are damaged by water ingress.
PCB & Internal Issues - Worcester Boiler Fault Codes
Typical Cause:
Internal components are failing to communicate with the PCB.
What to do:
- Power-cycle the boiler once.
Call an engineer if:
- PCB or wiring faults are present.
- Internal components not communicating correctly.
Typical Cause:
Incoming mains voltage too low for safe boiler operation.
What to do:
- Check other appliances for low voltage issues.
- Reset boiler once.
Call an engineer if:
- Voltage issues persist or internal PCB may be damaged.
Typical Cause:
General PCB or internal electronics fault.
What to do:
- Reset boiler once.
Call an engineer if:
- PCB replacement or professional inspection required.
When to Call a Professional
Keep Your House Safe
While some minor boiler issues can be safely checked by a homeowner, many Worcester Bosch boiler fault codes require expert attention. You should always contact a Gas Safe registered engineer in the following situations:
- Repeated fault codes or lockouts (EA, E1, E5, F0–F9).
- Boiler pressure keeps dropping or system leaks are visible.
- No heat or hot water despite the boiler running.
- Strange noises (banging, gurgling, whistling).
- Unusual smells, especially gas or burning.
- Condensate pipe frozen, blocked, or causing internal water backup.
- Pump not circulating water properly.
- Electrical faults, PCB errors, or sensor malfunctions.
- Gas valve or ignition problems.
Safe to DIY: Resetting the boiler, topping up pressure, bleeding radiators, or clearing minor external ice.
Does the Worcester Guarantee Cover Error Codes?
Warranty protected
The guarantee can cover Worcester Bosch boiler fault codes if they are caused by a manufacturing defect or faulty boiler part. Coverage applies during the warranty period and requires:
- PCB / circuit board
- Sensors (flow, return, NTC)
- Internal pump
- Ignition electrodes
- Any manufacturing defects causing repeated error codes
- Blocked or frozen condensate pipes.
- Poor installation, incorrect maintenance, or accidental damage.
- Gas supply or user errors (e.g., topping up wrong, resetting too often).
Not covered:
Warranty covers the faulty parts causing the error code, not user-caused issues like frozen pipes or leaks.
Our Servicing Areas
for Worcester boiler fault codes
If you’re having trouble with your Worcester Bosch boiler, we’re here to help with fast, reliable diagnostics and repairs. We proudly support homeowners and landlords across Ely , Soham , Littleport , Burwell , Newmarket, Fordham , Mildenhall and Waterbeach. Whether it’s a simple reset, a recurring Worcester Bosch boiler fault code, or a more complex breakdown, you can count on us to get your heating running smoothly again.
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