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Worcester Bosch Fault Codes
Worcester Bosch Fault Codes: What They Mean And What To Do
Reviewed by our Gas Safe registered engineers · Last updated 21 July 2026
Worcester Bosch is the brand we’re asked about most in North London, largely because it’s what most new-build flats and recent installs have fitted. Codes vary more between generations than most brands — older Greenstar models use simple letter-number codes, while newer Greenstar 8000 and Ei-series models show more detailed alphanumeric codes with a description on screen.
Quick answer: D5 and low-pressure codes (like 224) are usually fixable by repressurising via the filling loop. EA 229 and C6 codes relate to ignition and the fan — these are safety lockouts that shouldn’t be repeatedly reset without a proper look from an engineer.
Common Codes
Common Worcester Bosch fault codes
The codes below cover the ones we’re called out for most often. If yours isn’t listed or your display shows something different, note the exact wording and call us.
| Code | Meaning | First step |
|---|---|---|
| D5 | No water flow detected | Check system pressure and any closed valves |
| EA 229 | Ignition lockout | One reset can be tried; don’t repeat if it recurs |
| C6 | Fan fault | Needs an engineer — not something to reset repeatedly |
| 224 (low pressure) | Low system pressure (newer Greenstar 8000/Ei models) | Repressurise via the filling loop |
| Code | Meaning | First step |
|---|---|---|
| A1 | Pump stuck or running dry | Check pressure is around 1–1.5 bar; if normal, needs an engineer |
| C6 | Fan speed fault | Needs an engineer — fan or wiring |
| C7 | Fan not running at start-up | Needs an engineer — fan or wiring |
| CC | Outdoor sensor fault | Needs an engineer — sensor or wiring |
| D5 | No water flow detected | Check system pressure and any closed valves |
| E9 | Overheat / high-limit thermostat tripped | Don’t keep resetting; book an engineer |
| EA | No flame detected on ignition | In cold weather often a frozen condensate pipe; otherwise call an engineer |
| EA 229 | Flame signal lost during operation | One reset can be tried; if it recurs, needs an engineer |
| EA 338 | No flame established on start-up | Check the gas is on; if it recurs, needs an engineer |
| FA | Flame detected after the gas valve closed | Safety fault — call an engineer, don’t reset repeatedly |
| F7 | Flame signal present before the burner starts | Needs an engineer |
| FD | Reset pressed by mistake or power lost during lockout | Reset once; if it recurs, needs diagnosis |
| H07 | Low water pressure warning | Repressurise via the filling loop to around 1–1.5 bar |
| 224 | Low system pressure (Greenstar 8000/Ei) | Repressurise via the filling loop |
| D4 | Flow temperature rising too fast | Often circulation related — call an engineer |
Engineer Advice
What we see most often with Worcester Bosch boilers
- The Greenstar range is generally very reliable, but the diverter valve on combi models is a known wear part — worth checking if your hot water becomes inconsistent.
- Newer Ei-series boilers display a plain-English description alongside the code. Read the full message, not just the code number.
- The 7-year and longer warranties Worcester Bosch offers on many models require proof of annual servicing by a Worcester-accredited installer to stay valid.
What Repairs Typically Cost
Typical Worcester Bosch repair costs
Figures are general guidance for North London; the exact cost depends on your specific Greenstar model and the part needed. We quote before any work begins.
FAQs
Worcester Bosch fault codes — your questions answered
Why does my newer Worcester Bosch show a different style of code to my old one?
Worcester Bosch updated its diagnostic system with the Greenstar 8000 and Ei-series ranges, which show more descriptive on-screen messages than the older simple letter-number codes on earlier Greenstar models.
Does resetting a Worcester Bosch boiler void the warranty?
No, using the boiler’s own reset button as intended doesn’t affect the warranty. What can affect it is missing an annual service, since most Worcester warranties require proof of servicing by an accredited installer.
Is D5 always about mains water pressure, or could it be internal?
It usually points to internal system pressure or a flow restriction rather than mains water pressure specifically, since D5 relates to the central heating circuit rather than the incoming water supply.
Can a Worcester Bosch boiler show a fault code from a connected smart control rather than the boiler itself?
Yes — if you have a Wave or similar connected control, occasionally an issue with the control’s connection can surface as a related message, so it’s worth checking the control’s own app or display too.
Why would my boiler lock out with EA 229 repeatedly on the same day?
Repeated ignition lockouts on the same day usually mean an underlying issue with the ignition electrode, gas valve or gas supply pressure that a single reset won’t resolve — worth booking an engineer rather than continuing to reset.
Do all Worcester Bosch models use the same fault code numbering?
No — the numbering differs between the Greenstar CDi/i range and the newer 8000/Ei-series, so it’s worth checking your specific model when looking up a code.
Is C6 something that can be temporarily worked around?
No, a fan fault is a safety-relevant lockout and shouldn’t be worked around — the boiler won’t fire safely until the fan issue is resolved by an engineer.
Does Worcester Bosch’s long warranty cover parts and labour, or just parts?
Worcester Bosch’s standard and extended warranties typically cover both parts and labour for manufacturing faults, though the exact terms depend on the specific model and warranty length registered at installation. It’s worth checking your certificate, since some extended warranties have conditions around who can carry out the annual service that keeps the cover valid.
If my Worcester Bosch boiler is out of warranty, do repairs become significantly more expensive?
Not necessarily — an out-of-warranty repair costs the same as it would for any boiler needing that fix. The difference is simply that you’re covering the cost yourself rather than having it covered, so it’s worth weighing frequent repairs against replacement if your boiler is both out of warranty and getting on in years.
Related
More help and our repair service
The other brand we’re asked about most, with its own ecoTEC F-code system.
Read guide Fault CodesIdeal Boiler Fault CodesIdeal’s Logic and Vogue fault codes, explained in plain English.
Read guide Boiler ProblemsBoiler Not Igniting / LockoutWhat sits behind an EA 229 ignition lockout, and what’s safe to try.
Read guide PressureBoiler Losing PressureBehind a D5 or 224 code: why pressure keeps dropping and how to fix it.
Read guide MaintenanceAnnual Boiler Service GuideKeep your Worcester warranty valid with proof of annual servicing.
Read guide Buying GuidesNew Boiler Cost LondonWhen a repair stops being worth it versus replacing the boiler.
Read guideBrowse the full Boiler Fault Code Library for other brands, or head back to the Help & Advice Centre. We repair Worcester Bosch boilers across North London — see our boiler repair service, and keep yours covered with annual boiler servicing.
Got a Worcester Bosch fault code we haven’t listed?
Call us with the exact code and message shown, and we’ll tell you honestly what it means — and what it will cost to put right. Same-day appointments subject to availability.
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