How does a Greenstar show a fault?
A Greenstar shows a fault as a two-character code with a numeric cause code on its display, or as a flashing blue light on models without a display. Worcester Bosch has used three display styles over the last twenty years.
- Greenstar i, Si and CDi (roughly 2005-2020). A small display shows a two-character code such as EA, E9 or CE and a three-digit cause code such as 227. A blue burner light sits next to the dial.
- Greenstar 2000, 4000, 8000 Life and Style. A text display shows the code, the cause number and a short message; many cause numbers now have four digits, and bosch boiler error codes on the same platform follow the same pattern.
- Greenstar Ri and older models without a display. The blue light is all you get.
Photograph the display before resetting. For other brands, see our boiler fault code guide.
What do EA, 227, 224, A1, D5 and the other common codes mean?
EA 227 is no flame at ignition, E9 224 an overheat limiter, CE 207 low water pressure and A1 281 a pump fault; D5 is not consistently documented. The meanings below are summarised from Greenstar user and installation manuals; where we could not confirm a code against a manual we say so.
| Code | Meaning (per Greenstar manuals) | Can you clear it? |
|---|---|---|
| EA 227 | No flame detected during ignition (no ionisation signal); the boiler locks out after its ignition attempts | Often: gas supply, meter credit, condensate pipe, then one reset |
| EA 229 | Flame lost while the burner was running | Same checks; engineer if it repeats |
| E9 219 | Safety temperature sensor exceeded its limit (overheating) | Cool down, check pressure, one reset; then engineer |
| E9 224 | Temperature limiter on the heat exchanger or flue gas has activated | As E9 219; repeated 224 means a circulation or sensor fault for an engineer |
| CE 207 | System water pressure too low (newer displays may show a four-digit code such as 1017) | Yes: top up to 1-1.5 bar |
| A1 281 | Pump running dry or stuck | Check pressure, top up, one reset; engineer if it returns |
| C6 215 | Fan speed outside limits | No: engineer |
| C7 214 | Fan not running | No: engineer |
| E2 222 | Flow temperature sensor fault | No: engineer |
| D1 240 | Return temperature sensor fault | No: engineer |
| D5 | Not documented consistently across models; some guides link it to a blocked condensate or flue path | Check the condensate pipe, one reset; then engineer with the manual for your model |
| F7 228 | Flame detected while the burner should be off | No: switch off and call an engineer |
| A21 | Commonly listed as a communication fault with a wireless control; check your manual | Check thermostat batteries and range, re-pair |
| 1021, 1101, 2951 | Cause codes on 4000/8000 displays we could not confirm from manuals | Photograph the display and call an engineer |
A Worcester boiler EA code covers everything from an empty prepayment meter to a failed gas valve; the cause number separates them.
Why is the blue light flashing?
On Greenstar i, Si and CDi models the blue light is the burner-on indicator: steady blue means the burner is lit, flashing blue means the boiler has locked out on a fault. On a boiler with a display the code appears alongside; on a Greenstar Ri or an older model without a display, the flashing blue light is the lockout signal on its own.
Two related signals confuse owners. A red or flashing reset button, which some Greenstar models use, is the same lockout message in a different place. A flashing radiator or tap symbol on the newer text displays is a status indication, not a fault. If the blue light is flashing, work through the checks below and reset once at the end.
What are the likely causes behind each code?
Most Worcester lockouts trace back to the gas supply, a frozen condensate pipe or low pressure; the table ranks the causes for each code family.
| Code family | Most likely causes, in order | Who fixes it |
|---|---|---|
| EA 227 ignition failure | Prepayment meter out of credit; gas isolation valve closed; gas supply interrupted; frozen or blocked condensate pipe; worn ignition electrode or lead; faulty gas valve | You for the first four; engineer for the last two |
| EA 229 flame loss | Gas supply dip; frozen condensate pipe; flue recirculation in strong wind; electrode or gas valve | Mostly engineer unless the condensate pipe is the cause |
| E9 219, E9 224 overheat | Low pressure or airlock; pump failing; sludge in the heat exchanger; faulty sensor | You for pressure and bleeding; engineer for the rest |
| CE 207, 1017 low pressure | Normal slow loss; recent radiator bleeding; small leak at a valve or joint; passing pressure relief valve; flat expansion vessel; failed pressure sensor (gauge reading normal) | You for the top-up; engineer if it repeats within weeks |
| C6, C7 fan | Fan motor; blocked flue; control board | Engineer |
| No code, heating works, no hot water | Stuck diverter valve; scaled plate heat exchanger; hot water sensor | Engineer |
A Worcester combi with no hot water but a normal display is rarely a code problem; our guide to no hot water from a boiler works through the diverter valve and thermostat possibilities.
Which steps can you safely try yourself?
Check the pressure, gas supply, condensate pipe and controls, then reset once. A filling loop is the short hose or link with two valves under the boiler that tops up the heating water from the mains; none of these steps involves the casing or the gas pipework.
- Read and photograph the code. Note the two-character code and the cause number, and whether the blue light or reset button is flashing.
- Check the pressure gauge. With the heating off, the needle should sit at 1-1.5 bar. Below about 0.5 bar you will see CE 207 or 1017; A1 and E9 can also follow low pressure.
- Top up if needed. Open the filling loop valves slowly until the gauge reads 1-1.5 bar, then close both fully. CDi Compact and i Junior models use a white plastic filling key instead of a braided loop; our guide to Worcester Bosch boiler pressure shows both.
- Check the gas supply. Does the hob or gas fire light? Is there credit on a prepayment meter? Is the yellow-handled gas isolation valve under the boiler open (handle in line with the pipe)? Any of these produces EA 227.
- Check the condensate pipe in freezing weather. If the white plastic pipe outside is frozen, the boiler often gurgles before showing EA. Pour warm, never boiling, water along the pipe; our guide to a frozen condensate pipe explains how.
- Check the controls. Thermostat above room temperature, programmer in the right mode, fresh batteries in a wireless stat.
- Check the isolation valves. The flow and return valves under the boiler should be open; a half-closed valve can trigger overheat codes.
- Reset once. Press the reset button as the manual describes and give the boiler three minutes. The sequence for each generation is in our guide to resetting a boiler.
If the code stays away, note the date. If it returns the same day, stop.
Does it matter which Greenstar you have?
Only for reading the display: the code meanings and the safe checks are the same across generations. If the boiler is within its guarantee and has been serviced annually, call Worcester's own service team rather than a local firm; the brand review of Worcester Bosch boilers lists the ranges and guarantee terms.
On older models with a mechanical gauge, a Worcester pressure gauge not working, stuck at one reading whatever you do, may itself be faulty, so ask an engineer to confirm the true pressure before relying on it. Most Worcester Bosch boiler problems, from fault 227 to the flashing blue light, are the same few faults wearing different clothes.
What if the reset does not clear the code?
A Worcester reset not working means the fault has moved to the engineer's side of the casing. If the code comes straight back, the cause is still present: no gas, a frozen pipe, or a failed part. If the boiler runs for an hour and locks out again, a weak electrode, a struggling fan or an intermittent gas valve is likely.
Repeated lockouts on a boiler over twelve to fifteen years old change the question from "what is the part" to "is the part worth it". Fans, gas valves and heat exchangers each run into several hundred pounds fitted, and once one has gone the others are rarely far behind. Our guides to how long a boiler lasts and repairing or replacing a boiler set out the arithmetic, and the new boiler cost guide gives the fitted price ranges to compare against the repair quote.
Frequently asked questions
What does EA 227 mean on a Worcester boiler and how do I fix it?
EA 227 means the boiler tried to ignite and did not detect a flame, so it locked out. The safe fixes are all about supply: check another gas appliance lights, check a prepayment meter has credit, check the gas isolation valve under the boiler is open and, in freezing weather, thaw the condensate pipe with warm water. Then press reset once. If EA 227 returns, the ignition electrode, lead or gas valve needs a Gas Safe registered engineer.
Why is the blue light flashing on my Worcester boiler?
On Greenstar i, Si and CDi models the blue light is the burner indicator. Steady blue means the burner is lit and all is well. A flashing blue light means the boiler has locked out on a fault; on models with a display the code appears alongside, and on models without one, such as the Greenstar Ri, the flashing light is the only signal. Note any code, do the safe checks and reset once.
What is Worcester fault 224?
The 224 cause code accompanies E9 and indicates that a temperature limiter has activated because the heat exchanger or flue gas ran too hot. Related codes are E9 219 (safety temperature sensor exceeded its limit) and E5 218 (flow temperature too high). Low pressure, an airlock or a struggling pump are common triggers. Check the pressure, bleed the radiators and reset once; if it comes back, book an engineer rather than resetting again.
Why does my Worcester boiler have no hot water but the heating works?
If there is no fault code, the usual suspect on a combi is the diverter valve, which switches the boiler between heating and hot water and can stick on the heating side. A blocked plate heat exchanger in hard-water areas and a failed hot water sensor produce the same symptom. None of these is a user fix. If a code is showing, deal with that first, as a lockout stops both heating and hot water.
What do Worcester codes 1021, 1101 and 2951 mean?
These four-digit cause codes appear on the newer Greenstar 2000, 4000 and 8000 displays. We could not confirm a single documented meaning for them from Worcester manuals, and online explanations conflict, so we do not guess. Photograph the display, check the pressure and gas supply as usual, and give the exact number to a Gas Safe registered engineer or the Worcester Bosch technical helpline.
How many times can I reset a Worcester boiler?
Once, after you have fixed the obvious cause. A second reset the same day is reasonable if the boiler ran normally in between. Beyond that, repeated resetting on an ignition code can leave unburnt gas in the combustion chamber and masks a fault that is getting worse. If the code returns within a day, or you are resetting more than once a week, stop and call a Gas Safe registered engineer.
Sources and further reading
- Worcester Bosch - homeowner support
- Worcester Bosch - Greenstar user and installation manuals (literature downloads)
- Gas Safe Register - find or check an engineer
- HSE - Domestic gas health and safety
Prices and scheme details were checked on 22 October 2026 and are shown as typical ranges. Always get written quotes from Gas Safe registered installers.