Our Expert Guide to Fault Codes on Worcester Boilers
Is your Worcester boiler showing an error? Identify the fault and get your heating back on.
If your Worcester Bosch boiler has stopped working, it is likely displaying a specific fault code (like EA, U9, or C6). While some issues can be resolved with a simple system reset, others require a Gas Safe registered engineer to ensure your home remains safe.
As Wokingham’s leading Worcester Bosch specialists, we’ve compiled this guide to help you understand what your boiler is telling you—and when it’s time to call in the professionals.
Worcester Bosch Troubleshooting: 10 Common Faults & Wokingham Repair Advice
Is your Worcester Bosch boiler misbehaving? At Thermotec, we’ve spent over 20 years masterfully diagnosing heating issues throughout Wokingham and Berkshire. Before you panic, use our local expert guide to identify the culprit and find out if it's a simple DIY fix or a job for a Gas Safe specialist.
1. The "Low Pressure" Drop
Check your needle. If it’s fallen below the 1.0 bar mark, your boiler will likely shut down to protect itself. While you can usually repressurise a Worcester system using the internal filling key or external loop, a needle that keeps diving suggests a hidden leak within your pipework or a failing expansion vessel.
2. Visible Water Leaks
Water and electricity are a dangerous mix. If you see drips beneath the casing, your internal seals or the heat exchanger may be compromised. Left ignored, moisture will fry the PCB (the boiler's brain), turning a minor repair into a major expense. Shut off the power and call us immediately.
3. "Kettling" or Heavy Vibrations
Does your boiler sound like a whistling kettle? This is "Kettling," usually caused by limescale or sludge trapped in the heat exchanger. It forces the boiler to work harder, spiking your energy bills. A professional MagnaCleanse or Powerflush is the only way to restore quiet, efficient operation.
4. Safety Lockouts (Ignition Error EA)
If you see Error 227, your boiler has attempted to light and failed. This is often a gas valve issue or a fouled sensing electrode. If one reset doesn’t clear it, don't keep trying—the system is locking you out for your own safety.
5. The Winter "Ice Block" (Condensate Pipe)
During freezing Berkshire nights, the plastic pipe running outside can freeze solid. This causes a backup of water that "chokes" the boiler. Pro-tip: Carefully pour warm (never boiling) water over the external pipe to melt the ice and hit reset.
6. Critical Overheating
If the casing feels hot to the touch or you smell "hot dust," your circulating pump or fan might have seized. An overheating boiler is under immense pressure; turn it off at the wall to prevent the heat exchanger from cracking.
7. "Dead" Display (No Power)
Before assuming the boiler is broken, check your consumer unit (fuse box). If the RCD hasn’t tripped, the fault likely lies in a blown fuse on the PCB. We carry specialized diagnostic tools to pinpoint exactly where the circuit has failed.
8. The "Diverter Valve" Glitch (No Hot Water)
If your radiators are piping hot but your taps stay cold, your diverter valve is likely stuck. This is a common quirk in older Worcester Greenstar models. We stock genuine Bosch parts to ensure we can often fix this in a single visit.
9. Ineffective or Patchy Radiators
If your radiators are stone cold at the bottom, you have a build-up of heavy iron oxide "sludge." If they are cold at the top, they simply need bleeding. If the entire system is lukewarm, your central heating pump is likely losing its flow strength.
10. Short Cycling (Frequent On/Off)
If your boiler fires up for two minutes and then shuts down, it’s "short cycling." This is usually a sign of an oversized boiler, a faulty thermostat, or a total lack of water circulation. It’s a silent killer for boiler longevity and a major drain on your wallet.
Common Worcester Boiler Fault Codes Explained
Every Worcester model has a "language" of its own. Here is what your display is trying to tell you:
CDi Classic (Code A1): This signals a potential water leak or a pump that has reached the end of its life.
Greenstar i (Code EA): The most common error. It means a flame hasn't been detected. Check your gas supply first; if that's fine, the ignition electrode is likely faulty.
Compact / Si Models (Code C7): This indicates the fan is not operating correctly, preventing harmful gases from being vented safely.
Greenstar 8000 (Code 202): Your boiler is in "anti-cycle mode." This isn't a fault; the boiler is simply resting to prevent overheating. Wait 15 minutes for it to restart.
Greenstar Ri (Slow Flashing Light): This is a general ignition lockout. If a reset doesn't work, a Gas Safe engineer needs to check the flue and gas pressure.
My Worcester Boiler is still not working—What now?
If you have tried resetting your boiler and checked your system pressure, but the fault code remains, do not attempt to open the boiler casing yourself.
Thermotec provides rapid-response boiler repairs across Wokingham and Berkshire.
Specialist Tools: We carry the latest diagnostic equipment for all Worcester Bosch models (Greenstar, Ri, iJunior).
Genuine Parts: We only use manufacturer-approved parts for lasting reliability.
Fixed-Price Repairs: No hidden costs. We diagnose the fault and give you a clear price to fix it.
Worcester Bosch Boilers: Frequently Asked Questions
1. Why is my Worcester boiler showing a blue flashing light?
A flashing blue light is a general warning that the boiler has encountered a fault. If it is accompanied by an EA error code, it usually means the flame has failed—check your gas supply or meter credit first. If the light is pulsing slowly without an error code, the boiler may simply be in a "service mode" and might just require a standard reset.
2. How often should I service my Worcester Bosch boiler?
To maintain your manufacturer’s warranty and ensure peak efficiency, you must have a Gas Safe service every 12 months. Regular servicing prevents common issues like heat exchanger blockages and allows us to check that internal seals are still watertight, protecting your expensive electronics from leaks.
3. My Worcester boiler pressure keeps dropping—what is wrong?
If you have to use the filling loop more than once or twice a year, you likely have a leak. This could be a visible drip from a radiator valve or a hidden issue like a failing expansion vessel or a leaking Pressure Relief Valve (PRV). Constant topping up introduces fresh oxygen into the system, which causes internal rust and corrosion.
4. How do I reset my Worcester Greenstar boiler?
For most modern Greenstar i, Si, and CDi models, press and hold the 'Reset' button for 3 to 5 seconds. On the newer Greenstar 8000 series, you must use the digital touch-screen menu. If the fault code returns immediately after a reset, do not keep trying; a safety component has likely failed and requires a Gas Safe engineer.
5. What is the average lifespan of a Worcester Bosch boiler?
With annual servicing, a Worcester Bosch boiler typically lasts between 12 and 15 years. If your unit is over a decade old and requiring frequent, expensive repairs, it is often more cost-effective to upgrade to a modern A-rated system, which can significantly reduce your monthly energy bills.
6. Why are my radiators hot at the bottom but cold at the top?
This is almost always caused by trapped air in the system. You can usually resolve this yourself by "bleeding" your radiators with a standard radiator key. However, if the radiators are cold at the bottom but hot at the top, this indicates a build-up of heavy "sludge," which requires a professional Powerflush to clear.
Worcester Bosch Boiler Manuals by Model
Need help using or troubleshooting your Worcester Bosch boiler? Access downloadable PDF manuals for a wide range of models — including installation, user, and servicing instructions.