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Worcester Bosch Fault Code Guide
Greenstar i, CDi Classic, Si Compact, 8000 & Ri — EA, A1, C6, C7, 202 and more explained plainly
Your Worcester Bosch boiler has locked out to protect itself. This guide covers every common fault code across the Greenstar range — what each means, what you can safely try yourself, and when to call a Gas Safe engineer. Thermotec is Wokingham’s Worcester Bosch specialist with over 20 years experience across RG40.
£96
Fixed
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diagnostic
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First-time
fix rate
fix rate
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Years
experience
experience
Same day
Where
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Boiler showing a fault code?
Fixed price · Genuine parts · Worcester specialist
Diagnostic fee£96
First-time fix90%
ResponseSame day
Fault code index
Worcester Bosch fault codes — full reference
Find your code below. Severity indicates whether you can attempt a fix yourself (Low/Info) or whether a Gas Safe engineer is required (High/Medium).
| Code | Fault | Common cause | Action | Severity |
|---|---|---|---|---|
| EA / 227 | No flame detected / ignition failure | Gas supply issue, faulty ignition electrode, frozen condensate pipe, fouled flame sensor | Check gas meter credit. Check condensate pipe for ice — thaw with warm water. Press Reset 3–5 seconds. If fault returns, call engineer. | High |
| A1 | Low pressure / pump fault | Water leak, failing pump, faulty pressure sensor | Check pressure gauge — repressurise to 1.5 bar using filling key/loop. If pressure keeps dropping, hidden leak or expansion vessel — engineer required. | High |
| C6 | Fan speed error | Fan motor failing, flue obstruction, wiring fault | Safety lockout — do not reset repeatedly. Harmful gases cannot be vented safely. Engineer inspection required. | High |
| C7 | Fan not operating correctly | Fan motor failure, flue blockage, wiring fault | Do not attempt to reset. Fan failure prevents safe venting — Gas Safe engineer required immediately. | High |
| U9 | Overheat / high temperature limit | Circulating pump seized, blocked heat exchanger, airlock, sludge build-up | Turn off at wall if casing feels hot. Do not restart. Pump or heat exchanger inspection required. | Medium |
| D5 | Diverter valve fault | Stuck or faulty diverter valve — common on older Greenstar models | Radiators heating but no hot water (or vice versa) is the symptom. Genuine Bosch part replacement required. | Medium |
| E9 | Safety temperature exceeded | Pump failure, blocked heat exchanger, very low water flow | Do not reset repeatedly. Engineer needed to inspect pump and heat exchanger. | Medium |
| 202 | Anti-cycle mode (not a fault) | Boiler resting to prevent overheating between firing cycles | This is normal behaviour. Wait 15 minutes — the boiler will restart automatically. No action needed. | Info |
| Slow flashing light | General ignition lockout (Greenstar Ri) | Ignition failure, gas supply issue, flue problem | Press Reset. If fault returns, engineer needed to check flue and gas pressure. | Medium |
Stuart’s pro tip for Wokingham homeowners
The most common Worcester fault call we get in winter is the EA code caused by a frozen condensate pipe. The small plastic pipe running outside your property can freeze solid overnight in Berkshire temperatures. Before calling an engineer, locate the pipe (usually white or grey plastic, runs outside and down a wall), and carefully pour warm — not boiling — water along it to thaw. Then press and hold the Reset button for 3–5 seconds. This resolves the fault at no cost in the majority of winter call-outs.
Troubleshooting guide
10 common Worcester Bosch problems explained
Before you call an engineer, work through these common faults — some can be resolved yourself, others are clear signals to stop and call immediately.
Fault 01
Low pressure drop
If the needle has fallen below 1.0 bar the boiler will shut down. Repressurise using the internal filling key or external loop to 1.5 bar. A needle that keeps dropping suggests a hidden leak or failing expansion vessel.
Fault 02
Visible water leaks
Drips beneath the casing mean internal seals or the heat exchanger may be compromised. Left unchecked, moisture will damage the PCB. Shut off the power and call an engineer immediately.
Fault 03
Kettling or heavy vibrations
A whistling kettle sound is kettling — limescale or sludge trapped in the heat exchanger. It forces the boiler to work harder and spikes your energy bills. A professional powerflush is the fix.
Fault 04
Ignition error EA / 227
The boiler has attempted to light and failed. Often a gas valve issue or fouled sensing electrode. One reset is acceptable — if the fault returns immediately, stop resetting. The system is locking out for safety.
Fault 05
Frozen condensate pipe
During freezing Berkshire nights, the plastic condensate pipe can freeze solid, choking the boiler. Pour warm (never boiling) water over the external pipe to melt the blockage, then hit reset.
Fault 06
Critical overheating
If the casing feels hot to the touch or you smell hot dust, the circulating pump or fan may have seized. Turn off at the wall immediately to prevent the heat exchanger from cracking.
Fault 07
Dead display (no power)
Check your consumer unit first — has the RCD tripped? If not, the fault likely lies in a blown fuse on the PCB. Specialist diagnostic tools are needed to pinpoint exactly where the circuit has failed.
Fault 08
Diverter valve glitch — no hot water
Radiators piping hot but taps stay cold? Your diverter valve is likely stuck — a common issue on older Greenstar models. We carry genuine Bosch parts for a same-visit fix in most cases.
Fault 09
Patchy or cold radiators
Cold bottom = iron oxide sludge. Cold top = trapped air (bleed the radiator yourself). Entire system lukewarm = the central heating pump is losing flow strength. See our radiator services.
Fault 10
Short cycling (frequent on/off)
The boiler fires for two minutes then shuts down. Usually an oversized boiler, a faulty thermostat, or a total lack of water circulation. A silent killer for boiler longevity — engineer diagnosis needed.
Model-specific codes
Worcester Bosch fault codes by model
Each Greenstar model has its own display language. Find your model below for the specific code it’s showing.
Greenstar i Combi
EA
The most common error. No flame detected — check gas supply first. If fine, the ignition electrode is likely faulty.
Download manual (PDF) →
CDi Classic Combi
A1
Signals a potential water leak or a pump that has reached the end of its life. Check pressure and look for drips.
Download manual (PDF) →
Greenstar Si Compact
C7
Fan not operating correctly — prevents harmful gases from being safely vented. Do not reset. Engineer required.
Download manual (PDF) →
Greenstar 8000 Life
202
Anti-cycle mode — not a fault. The boiler is resting to prevent overheating. Wait 15 minutes and it will restart automatically.
Download manual (PDF) →
Greenstar Ri / Junior
Slow flashing light
General ignition lockout. Press reset. If fault returns, a Gas Safe engineer needs to check the flue and gas pressure.
Download manual (PDF) →
Greenstar 4000
EA / C6
EA indicates ignition failure. C6 indicates fan speed error. Both require engineer diagnosis if a reset doesn’t clear the fault.
Download manual (PDF) →
PDF manuals
Download Worcester Bosch manuals
User, installation and servicing manuals for all major Greenstar models. Click to download direct.
Common questions
Worcester Bosch FAQ — Wokingham
Why is my Worcester boiler showing a blue flashing light?
A flashing blue light is a general fault warning. If accompanied by an EA code, the flame has failed — check gas supply or meter credit first. If pulsing slowly without an error code, the boiler may be in service mode and need a standard reset.
How do I reset my Worcester Greenstar boiler?
On most Greenstar i, Si and CDi models, press and hold the Reset button for 3–5 seconds. On the Greenstar 8000 series, use the digital touchscreen menu. If the fault code returns immediately after a reset, stop resetting — a safety component has likely failed and needs a Gas Safe engineer.
My Worcester boiler pressure keeps dropping — what’s wrong?
If you’re using the filling loop more than twice a year, you likely have a leak. Could be a visible radiator valve drip, a failing expansion vessel, or a leaking Pressure Relief Valve. Constant topping up also introduces oxygen that causes internal corrosion. Book a diagnostic to find the root cause.
How often should I service my Worcester Bosch boiler?
Annually. A Gas Safe service every 12 months maintains your manufacturer’s warranty, prevents heat exchanger blockages and checks that internal seals are still watertight — protecting your electronics from moisture damage. See our annual boiler service page.
What is the average lifespan of a Worcester Bosch boiler?
With annual servicing, 12–15 years is typical. If your unit is over a decade old and requiring frequent expensive repairs, upgrading to a modern A-rated system often makes more financial sense — see our new boiler installation page.
Why are my radiators hot at the bottom but cold at the top?
Almost always trapped air — bleed the radiators with a standard radiator key, this is a DIY job. If the radiators are cold at the bottom but hot at the top, that’s heavy sludge build-up which needs a professional powerflush to clear.
Related pages
More Worcester Bosch & boiler support
Worcester fault code won’t clear? Call Stuart.
Gas Safe 599015 · £96 fixed diagnostic · 90% first-time fix · Genuine parts · Same-day where available · Wokingham & RG40