Worcester Bosch boilers are a popular choice across the UK, known for their reliability and energy efficiency. Like any heating system, they can still develop faults.
Each model, from the Greenstar 1000 to the 8000 Life & Style series, has its own set of error codes that point to particular issues. Knowing these codes and their common causes supports quicker diagnostics, efficient maintenance, and safer running.
This guide covers the error codes for each major Worcester Bosch range, what typically causes them, and how to respond safely.
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Understanding Worcester Bosch Fault Code Types
Worcester Bosch groups its fault codes into a few broad categories, and knowing which type you’re looking at tells you a lot about how serious the situation is.
Fault or lockout codes, the alphanumeric codes covered throughout this guide, mean the boiler has stopped and needs the cause resolved before it will restart safely.
Blocking errors stop the boiler operating immediately but don’t always show a code on the display, often linked to a blockage somewhere in the system such as the condensate pipe.
Maintenance codes begin with the letter H followed by a number. The boiler keeps running when one of these appears, but it’s a signal that a qualified engineer should take a look before a minor issue develops into a costlier fault.
Worcester Bosch Error Codes by Model
Greenstar 1000, 2000, and Greenstar i Series
The Greenstar i was Worcester Bosch’s best-selling combi boiler for years, with more than a million installed across the UK, before being discontinued and replaced by the current Greenstar 4000 range. Many of the codes below still apply to both.
| Code | Meaning |
| A1 | Water leak detected or pump issue (frequent in Greenstar 1000 and 2000) |
| B1 | Code plug not detected (common in Greenstar i and older 2000 models) |
| C1 | Airflow interruption during operation (Greenstar 1000 and 2000) |
| D1 | Return temperature sensor error (seen across 1000 and i series) |
| F0 | Internal error, such as ignition board or PCB fault |
| F7 | False flame detection when the boiler is off |
| EA / 227 | Ignition failure, no flame detected after multiple attempts, often caused by frozen condensate pipes, faulty gas valves, or flame sensors |
| 1017 | Low water pressure (common across all models) |
| C7 | Fan not running during startup |
Greenstar 4000 Series
Understanding the Worcester Bosch 4000 combi boiler features helps put these codes in context, since the 4000 range now carries most of the Greenstar i’s old customer base.
| Code | Meaning |
| 227 | No flame detected after ignition attempts |
| 228 | Flame signal detected without an actual flame (sensor or valve issue) |
| 1017 | Low water pressure |
| 1021 / 1022 | Hot water temperature sensor faults |
| 2924 | Modulating gas valve fault |
| 2946 | Incorrect code plug detected |
| 208 | Maintenance reminder or chimney sweep mode |
| C7 | Fan failure during startup |
Greenstar 8000 Life & Style Series
| Code | Meaning |
| EA 227 | Ignition failure after repeated attempts |
| 224 | Safety temperature limiter tripped (overheating) |
| 1017 | Low water pressure |
| 1021 / 1022 | Hot water sensor failure |
| 2924 | Gas valve feedback or relay fault |
| 2946 | Code plug communication issue |
| 201–204 | Operational status or standby codes |
CDi Classic, Si Compact, and Other Models
| Code | Meaning |
| A7 | Hot water sensor defect |
| C6 | Fan running too fast or too slow |
| FA | Flame fault after gas shutoff |
| D5 | Condensate pump failure |
| D6 | Internal heat bank overflow |
If your CDi or Si Compact model is showing C6, the Worcester Bosch C6 error troubleshooting guide walks through targeted fixes for fan speed faults on this code specifically.
Key Faults and Their Common Causes
EA 227 and Ignition Failures
Frozen condensate pipes are a frequent cause, blocking exhaust flow and preventing startup. Gas supply issues, such as frozen meters or faulty valves, can also restrict ignition. Faulty flame sensors or dirty electrodes may prevent flame detection, while circuit board damage from leaks or moisture can disrupt ignition control. This fault is usually accompanied by a flashing blue light on the display, and the Worcester Bosch blue light issues guide covers what the different flash patterns mean.
Low Water Pressure (Code 1017 and Variants)
Low pressure is often caused by leaks in the system, faulty pressure relief valves, or user error, such as failing to repressurise after bleeding radiators. Cold weather can also make pressure fluctuations worse.
Troubleshooting and Preventative Tips
- Prevent frozen condensate pipes. Insulate them before winter, and defrost carefully if needed.
- Monitor boiler pressure regularly. Top it up when it drops below the recommended level, usually 1 to 1.5 bar.
Schedule annual servicing. A Gas Safe registered engineer should clean flame sensors, inspect gas valves, and check the electronics once a year.
- Replace faulty parts early. Pressure relief valves and condensate pumps are worth replacing at the first sign of trouble, before they cause further damage.
For a straightforward walkthrough, the how to reset a boiler guide covers the exact steps for Worcester Bosch models, which can clear minor faults without needing an engineer visit.
FAQs
Why won’t my Worcester Bosch boiler turn on?
This could be down to low water pressure (check the gauge for 1 to 1.5 bar), a frozen condensate pipe, or a faulty thermostat. Repressurise the boiler, defrost the pipe, or reset the thermostat. If the issue persists, contact a Gas Safe engineer.
Why is my Worcester Bosch boiler leaking water?
Leaks often result from a faulty pressure relief valve, damaged seals, or internal corrosion. Turn off the boiler and call a professional to inspect and repair it. Regular maintenance helps prevent leaks by catching wear before it becomes a bigger issue.
Why is my Worcester Bosch boiler making strange noises?
Banging or whistling sounds may indicate trapped air, low pressure, or limescale build-up in the heat exchanger. Bleed the radiators, check the pressure, or book a service to descale the system.
What should I do if my Worcester Bosch boiler shows low pressure?
Low pressure is usually caused by system leaks or not repressurising after maintenance. Use the filling loop to top up the pressure. If it keeps dropping, consult an engineer.
Why is my Worcester Bosch boiler not producing hot water?
A faulty diverter valve, broken thermostat, or limescale build-up could be the cause. A Gas Safe engineer can diagnose and replace the faulty parts.
Why does my Worcester Bosch boiler keep switching off?
Frequent shutdowns may be due to overheating, low pressure, or a frozen condensate pipe. Check the pressure, defrost the pipe, and call a professional if the problem continues.
What does an ignition failure error mean on my Worcester Bosch boiler?
This error often points to frozen condensate pipes, a faulty gas valve, or a flame sensor issue. Defrost the pipe and make sure the gas supply is active. If it stays unresolved, contact an engineer.
How often should I service my Worcester Bosch boiler?
Annual servicing by a Gas Safe registered engineer is essential for maintaining efficiency, safety, and warranty compliance.
Why are my Worcester Bosch radiators cold at the top?
This is usually caused by trapped air in the radiators. Bleed them using a radiator key to restore even heating.
Can I fix Worcester Bosch boiler issues myself?
You can handle simple tasks like topping up pressure or bleeding radiators, but more complex issues should always be addressed by a Gas Safe engineer to ensure safety and a proper repair.
Is the Greenstar i still supported if mine develops a fault?
Yes. Although the Greenstar i has been discontinued in favour of the Greenstar 4000, parts and servicing support are still widely available, and most of the fault codes in this guide still apply.
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I’m Penny North, a home energy heating expert. My mission is to demystify new boilers and complex heating systems to help you achieve a warm, cosy home with lower energy bills and a smaller environmental footprint.