A Worcester Bosch fault code is the boiler diagnosing itself. Greenstar models usually show a fault code plus a cause code. An example is EA with 229. The pair identifies the problem. We take these meanings from the official Greenstar i ErP manual. EA 227 means no flame was detected after ignition. EA 229 means the flame signal was lost during operation. E9 224 means the safety thermostat has activated. A1 281 means the pump is stuck or running dry. Newer models use H07 for low system water pressure. Homeowners can often check and repressurise the system if their manual permits. You can also thaw a frozen external condensate pipe with warm water. You may reset the boiler once if instructed. Recurring codes always need a Gas Safe registered engineer. Do not attempt DIY on anything involving gas or combustion.
One honest note before the tables. Codes vary between Worcester Bosch models and generations. The same letter can carry different cause codes on different appliances. The meanings below come from the official Greenstar i ErP installation and servicing instructions (document 6 720 806 944). We note newer numeric codes where they appear. Your own boiler manual is the definitive reference for your exact model. You can also use the Worcester Bosch troubleshooting tool. Treat this list as a guide. It is not a substitute for the manufacturer instructions.
- Worcester Bosch Greenstar boilers display both a primary fault code (e.g. EA, E9) and a 3-digit numeric cause code (e.g. 227, 229).
- EA 227 and EA 229 signal ignition or flame failure, commonly caused by frozen condensate pipes or gas supply issues.
- Codes beginning with ‘H’ (such as H03) are maintenance service reminders rather than active mechanical breakdowns.
- What competitors miss: repeatedly resetting an EA lockout without curing a frozen condensate pipe risks flooding the combustion chamber.
- If repressurising or thawing an external condensate line doesn’t clear the fault, call our West London Gas Safe team for precision diagnosis.
How Worcester Bosch fault codes work
Worcester Bosch boilers signal problems in different ways. The manual is explicit about the difference. A blocking error stops the appliance temporarily. It clears by itself once the underlying condition resolves. This happens if an area needs to cool down. A locking error shuts the boiler down completely. It will not run until it is reset or repaired. The boiler keeps a history of the last eight faults.
Codes beginning with H are maintenance messages rather than breakdowns. On the Greenstar i ErP, H03 means the operating hours set for the service interval have expired. It works like a service light in your car. Booking an annual boiler service and resetting the reminder clears that message properly.
Ignition and flame codes
This is the largest family of codes. The boiler either failed to light or lost its flame. Older Greenstar i and CDi models show these as letter codes. The newer Greenstar 8000 style boilers use numbers for the same faults.
EA 227
No ionisation detected after ignition. The boiler tried to light and no flame signal followed.
Check other gas appliances work and the meter is on. Reset once if your manual instructs. Call an engineer if it returns.
EA 229
Loss of ionisation signal during operation. A flame was established and then lost.
The manual lists several possible causes. These include gas-air ratio and dynamic gas pressure. A frozen external condensate pipe is one possibility in cold weather. Reset once where instructed. Get an engineer if it returns.
F7 228
Ionisation current detected before burner start.
Engineer job. This is a flame-sensing fault.
FA 306
Ionisation detected after the gas valve closed.
Engineer job. This is a gas valve or sensing fault. Do not keep resetting this one.
EA 261
Control module potentially defective.
Reset once per the manual. Call an engineer if it persists.
Pressure, overheating and circulation codes
Homeowners can often help themselves with these codes. Most trace back to system pressure or water circulation.
A1 281
Pump stuck or running dry. The manual asks to check system water pressure and circulation.
Check the gauge. Repressurise if low and your manual permits. Call an engineer if the code stays.
E9 224
Flue or high-limit thermostat activated.
Check pressure is not very low. Then call an engineer.
E9 276
Primary flow temperature exceeded 95 degrees Celsius.
This is a protective shutdown that needs diagnosing. Do not repeatedly reset the boiler.
D4 341
Primary flow temperature rising too fast.
Check radiator valves are open. Then call an engineer.
H07 / 1017 W / 2971 B
Low system water pressure on newer models.
Repressurise to the pressure your manual specifies. This is typically 1 to 1.5 bar cold. Use the filling loop.
2970 B
Pressure dropping unusually fast.
Top up the system. Get the leak traced because that speed is not normal.
Sensor, fan and electronics codes
These are diagnostic codes rather than DIY fixes. They tell the engineer which component to investigate.
E2 222 / 223
Flow temperature sensor shorted or disconnected.
Engineer job. Sensor or wiring fault.
A7 808
Domestic hot water sensor defect.
Engineer job.
C6 215 / 216
Fan speed too high or too low.
Engineer job. The boiler will not fire safely without the fan.
C7 214
Fan does not run during the start-up phase.
Engineer job.
C7 217
Fan has stopped during appliance operation.
Engineer job.
C1 264
Fan stopped during operation.
Engineer job.
F0 238
Gas valve or control box error.
Try one reset if your manual instructs. Call an engineer if it returns.
F0 239 / 242 to 256
Control box or control module defective.
Engineer job.
Fd 231
The power was interrupted during a lockout.
Reset per the manual. Check what the lockout code was before it.
Meanings above are quoted from the official Worcester Bosch Greenstar i ErP instructions (document 6 720 806 944), verified July 2026. Other model families use different codes. Check the manual for your own appliance.
What you can safely do yourself
There is no universal list here. The safe actions depend on your model and what its manual permits. Read your own manual first.
Check and repressurise the system if your manual allows it. Top the system back up if the gauge is low. You might see A1 or H07. The target is commonly 1 to 1.5 bar cold using the filling loop. Worcester Bosch pressure guidance says topping up once or twice a year is normal. Our boiler losing pressure guide walks through it. It explains why repeated drops mean a fault.
Thaw an accessible frozen external condensate pipe. The condensate pipe carries slightly acidic water from the boiler to a drain. It can freeze in a cold snap and lock the boiler out. Pour warm water along it if you can safely reach the frozen section. Never use boiling water. Listen for the gurgle as it clears. Then reset per the manual. Lagging the pipe afterwards helps prevent a repeat. Leave it to an engineer if the pipe is out of reach.
Reset once where the manual instructs. Press and hold the reset button after dealing with a cause. Stop resetting if the same code comes straight back. Repeatedly clearing a lockout just delays the repair.
When to stop and call an engineer
Follow Gas Safe Register emergency steps if you smell gas. Get fresh air and open doors and windows. Turn off the gas emergency control valve at the meter. Do not turn the meter off if it is in a basement or cellar. Put out naked flames and do not smoke. Do not operate any electrical switches. They can ignite escaping gas. Call the National Gas Emergency line on 0800 111 999. Do not turn the gas back on until an engineer has checked it.
Any code that keeps returning needs a Gas Safe engineer. Combustion, fan, sensor and overheat faults require the right test equipment.
The code might involve gas, combustion, the fan or opening the boiler. Examples include an EA that will not clear or a repeated E9. These are never DIY territory.
Worcester Bosch is the brand we see most in homes across Kilburn, Queen’s Park and the surrounding area. Tell us the code and your model when you get in touch. A code narrows the diagnostic path considerably. It helps us arrive prepared. See boiler repairs for how we work.
Frequently asked questions
What does EA 229 mean on a Worcester Bosch boiler?
EA 229 is a loss of ionisation signal during operation. A flame was established and then lost. The boiler locked out for safety. The manual lists several possible causes. These include dynamic gas pressure and the flame probe. Have it diagnosed by a Gas Safe engineer.
Can I reset my Worcester Bosch boiler myself?
Yes, where your model manual instructs it. Resetting is the right move after dealing with a straightforward cause. Low pressure or a frozen condensate pipe are good examples. Reset once. Stop resetting if the same code returns.
What does E9 mean on a Worcester boiler?
E9 with cause code 224 means the flue or high-limit thermostat has activated. E9 276 means primary flow temperature exceeded 95 degrees Celsius. Both are protective shutdowns. The manual checks cover pressure, air and circulation. This is a Gas Safe engineer job.
Why does my Worcester Bosch keep showing a low-pressure code?
Topping up once or twice a year is normal. Sealed systems lose a little pressure over time. More often than that means water is escaping. You might have a small leak or a failing expansion vessel. Top up to 1.5 bar. Have the cause traced if it keeps dropping.
What do 1017, H07 or 2971 mean on a Worcester boiler?
They are low water pressure codes on newer Worcester Bosch models. They are the numeric equivalents of a gauge in the red. Repressurise the system via the filling loop and the code should clear. Have the leak traced if it comes back quickly.
Are Worcester Bosch fault codes the same on every model?
No. Codes and their cause codes vary between models and generations. The same problem can display differently on a Greenstar i and another model family. Use your own boiler manual for your exact appliance.
Worcester Bosch showing a fault code?
Send us the code and your model. It helps us turn up prepared.
- WhatsApp us: Book in 60 seconds
- Call 020 8051 2124. Our line is answered 24/7.
- See the service: boiler repairs
We are Gas Safe registered (657972). We repair Worcester Bosch, Vaillant, Ideal and most major brands across West and North West London. Heating that just works.
About the author Adam Said is a Gas Safe registered domestic gas engineer (657972) at The Happy Heating Co. He repairs Worcester Bosch and other major boiler brands in homes across West and North West London. This guide reflects what we see on real jobs every week.
Related reading
- Boiler repairs in West London
- Why is my boiler losing pressure?
- Annual boiler servicing
- How often should you service your boiler?
Code meanings are taken from the official Worcester Bosch Greenstar i ErP instructions and their troubleshooting tool, verified July 2026. Codes vary by model family. Always check the manual for your own appliance. Gas emergencies: National Gas Emergency line 0800 111 999.
