A Worcester Bosch fault code is the boiler diagnosing itself, and most codes point to one of a handful of problems. The ones we see most across West London: EA 229 (flame loss, in winter usually a frozen condensate pipe), EA (the boiler couldn’t ignite), E9 (the safety limiter has tripped on overheating), A1 (a pump problem, often linked to low pressure) and H07 (system pressure too low). There are exactly three fixes a homeowner can safely try: repressurise the system to 1–1.5 bar, thaw a frozen condensate pipe with warm water (never boiling), and reset the boiler once. Anything beyond that, and any code that keeps returning, is a job for a Gas Safe registered engineer. The Happy Heating Co (Gas Safe 657972) repairs Worcester Bosch boilers across West and North West London. See our boiler repairs service.
One honest note before the table: codes vary between Worcester Bosch models and generations. The list below covers the codes that come up most often, but your boiler’s manual, or Worcester Bosch’s own troubleshooting pages, is the definitive reference for your exact model.
How Worcester Bosch fault codes work
Worcester Bosch boilers signal problems in a few different ways. Some faults are blocking errors: the boiler pauses itself until a condition clears (a temporary issue like a pressure dip). Others are locking errors: the boiler shuts down and shows a flashing code until it’s reset or repaired. Codes starting with H are maintenance notices rather than breakdowns, and the SE code isn’t a fault at all: per Worcester Bosch’s own guidance, it appears after a set number of operating hours to say a service is due, the boiler equivalent of a service light in your car. Booking an annual boiler service clears that one properly.
Ignition and flame codes
The largest family: the boiler either couldn’t light, or lost its flame. On older Greenstar i and CDi models these show as letter codes; the newer Greenstar 8000-style boilers use numbers for the same faults.
| Code | What it means | What you can do |
|---|---|---|
| EA | The boiler tried to ignite and couldn’t; no flame detected | Check other gas appliances work and the meter isn’t off. Reset once; if it returns, engineer |
| EA 227 / 227 V | No flame signal after ignition; the burner lit briefly or not at all | As above: check gas supply basics, reset once, then engineer |
| EA 229 | Flame lost during operation. In cold snaps this is very often a frozen condensate pipe | Winter? Thaw the condensate pipe with warm water (below). Otherwise: reset once; if it returns, engineer |
| F7 | Flame detected before the burner should have lit | Engineer job: flame-sensing fault |
| FA / 306 V | Flame still detected after the gas valve closed | Engineer job: gas valve or sensing fault; don’t keep resetting this one |
| 228 V | Flame signal without a flame present | Engineer job: sensing electrode or PCB |
Pressure, overheating and circulation codes
These are the codes where a homeowner can often help themselves; most trace back to system pressure or water circulation.
| Code | What it means | What you can do |
|---|---|---|
| H07 / 1017 W / 2971 B | System water pressure too low | Repressurise to 1–1.5 bar via the filling loop |
| 2970 B | Pressure dropping unusually fast | Top up, but get the leak traced; that speed isn’t normal |
| A1 | Pump problem, running dry or stuck, often linked to low pressure | Check the gauge; repressurise if low. If the code stays, engineer |
| E9 / 224 V | Safety temperature limiter tripped; the boiler overheated | Check pressure isn’t very low; then it’s an engineer job (pump, blockage or circulation fault) |
| D4 | Flow temperature rising too fast; poor circulation | Check radiator valves aren’t all closed; then engineer |
Sensor, fan and electronics codes
Diagnostic rather than DIY; these tell the engineer which component to look at.
| Code | What it means | What you can do |
|---|---|---|
| E2 | Flow temperature sensor defective | Engineer job: sensor or wiring |
| A7 / 1021 B | Hot water temperature sensor defective | Engineer job |
| CC | Outdoor weather sensor not detected | Engineer job: sensor or connection |
| C6 | Fan running too fast or too slow | Engineer job; the boiler won’t fire safely without the fan |
| C7 | Fan not running at start-up | Engineer job |
| C1 | Fan stopped during operation | Engineer job |
| F0 | Internal electronics / gas valve control error | Try one reset (it can follow a power blip); if it returns, engineer |
| FD | Power interrupted, or the reset button held too long | Reset normally; usually clears itself |
| B1 | Code plug not detected (the boiler’s ID chip) | Engineer job: connection or plug |
| SE | Not a fault; service due after a set number of operating hours | Book a boiler service |
Meanings summarised from Worcester Bosch model documentation and official troubleshooting guidance, cross-checked against multiple published Greenstar code lists (July 2026); codes vary by model, always confirm against your manual.
The three fixes you can safely try yourself
1. Repressurise the system. If the gauge reads below 1 bar (or you’re seeing A1/H07), top the system back up to 1–1.5 bar cold using the filling loop. Worcester Bosch’s pressure guidance says topping up once or twice a year is normal. Our boiler losing pressure guide walks through it step by step, and explains why repeated drops mean a fault.
2. Thaw a frozen condensate pipe. The condensate pipe is the small plastic pipe carrying slightly acidic water from the boiler to a drain, often outside, where it can freeze in a cold snap and lock the boiler out (classically with EA 229). Pour warm, not boiling water along the frozen section, listen for the gurgle as it clears, then reset the boiler. Once it’s running, lag the pipe with foam insulation so it doesn’t happen again. It’s a two-pound fix for a recurring winter breakdown.
3. Reset the boiler, once. After fixing the cause, press and hold the reset button per your manual. If the same code comes straight back, or keeps returning over days, stop resetting: the boiler is telling you something is genuinely wrong, and repeatedly clearing the code just delays the repair.
When to stop and call an engineer
- You smell gas. Don’t touch the boiler or any switches. Call the National Gas Emergency line on 0800 111 999 immediately, open windows and get outside.
- Any code keeps returning after a reset. Combustion, fan, sensor and overheat faults all need a Gas Safe engineer with the right test equipment.
- The code involves gas, flame or the fan (EA that won’t clear, C6, repeated E9). These are never DIY territory.
Worcester Bosch is the brand we’re asked about most in homes across Ealing, Acton and the surrounding area, and most fault-code callouts are fixed in a single visit. Tell us the code when you get in touch; it usually tells us which part to bring. See boiler repairs for how we work, including our fixed pricing.
Frequently asked questions
What does EA 229 mean on a Worcester Bosch boiler?
EA 229 means the flame was lost while the boiler was running, and it’s locked out for safety. In winter the most common cause by far is a frozen condensate pipe; thaw it with warm (never boiling) water and reset. If it returns in mild weather, the cause needs a Gas Safe engineer.
Can I reset my Worcester Bosch boiler myself?
Yes. Pressing the reset button per your manual is safe, and it’s the right move after you’ve fixed a simple cause like low pressure or a frozen condensate pipe. Reset once. If the same code comes back, stop resetting and get it looked at: repeated lockouts mean a real fault.
What does E9 mean on a Worcester boiler?
E9 means the safety temperature limiter has tripped because the boiler overheated. It’s a protective shutdown, not a glitch; common causes are a failing pump, a blockage or circulation problem in the system. Beyond checking the pressure isn’t very low, this one is a Gas Safe engineer job.
Why does my Worcester Bosch keep showing a low-pressure code?
Once or twice a year is normal, per Worcester Bosch’s guidance; sealed systems lose a little pressure over time. More often than that means water is escaping: a small leak, a passing pressure relief valve or a failing expansion vessel. Top up to 1–1.5 bar, and if it keeps dropping, have the cause traced.
What do 1017, H07 or 2971 mean on a Worcester boiler?
They’re the low-water-pressure codes on newer Worcester Bosch models, the numeric equivalents of a gauge in the red. Repressurise the system to 1–1.5 bar via the filling loop and the code should clear. If it comes back quickly (or you see 2970, pressure dropping fast), have the leak traced.
Are Worcester Bosch fault codes the same on every model?
No. Codes vary between models and generations, which is why the same problem can show different codes on a Greenstar i and an older CDi. Use your boiler’s manual or Worcester Bosch’s troubleshooting pages for your exact model, and treat any general code list (including ours) as a guide.
Worcester Bosch showing a fault code?
Send us the code and your model; it usually tells us exactly what’s wrong and which part to bring.
- WhatsApp us — Book in 60 seconds
- Call 020 8051 2124. Our line is answered 24/7 and we’ll get your details to an engineer
- See the service: boiler repairs
We’re Gas Safe registered (657972) and repair Worcester Bosch, Vaillant, Ideal, Baxi and most major brands across West and North West London. Heating that just works, no drama.
About the author Adam Said is a Gas Safe registered domestic gas engineer (657972) at The Happy Heating Co, repairing 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 summarised from Worcester Bosch model documentation and their official troubleshooting guidance (verified July 2026); codes vary by model, always check your manual. Gas emergencies: National Gas Emergency line 0800 111 999.
