Worcester Bosch Boiler Fault Codes
Easy-to-understand explanations from your trusted local boiler experts.
See an error on your boiler?
Quickly find out what your Worcester Bosch is trying to tell you. Whether it's a one-off issue or a recurring fault, this guide explains the most common codes in plain English.
As Worcester Accredited Installers based in Crowborough, we help homeowners across Tunbridge Wells, Wadhurst, and nearby villages with honest advice and trusted boiler support.
👇 Scroll down to find the code you're seeing and learn what it means.
🟨 Worcester Bosch Greenstar i Series (e.g., 25i, 30i)
EA 227 – No flame detected
This usually means the boiler tried to light but couldn’t detect a flame. It might be caused by low gas pressure, a blocked flue, or an issue with the ignition.
Try resetting the boiler once. If the fault keeps coming back, it’s best to call us to check it safely.
C6 215 – Fan not running or running too slowly
The boiler’s fan isn’t working correctly. This fan helps remove gases from the flue — so when it fails, the boiler shuts down for safety.
Don’t ignore this one — it usually needs a proper check and may require a new fan or PCB.
D5 – Sensor fault
This code points to an issue with one of the boiler’s sensors — usually the flow or return temperature sensor.
It could be a loose connection or a faulty part. Best to get this looked at before it causes further problems.
E9 – Overheat or heat exchanger blocked
This means the boiler is running too hot, often due to poor water circulation or limescale in the system.
Turn off the boiler and let it cool down. Don’t keep resetting it — call us to investigate and prevent damage.
A1 – Low water pressure
This one’s common. Your boiler needs a certain pressure to run. Check the pressure gauge — if it’s below 1 bar, you can top it up using the filling loop.
If you’re unsure how or the pressure keeps dropping, give us a call — we’ll sort it quickly.
Worcester Bosch Greenstar Si Compact Fault Codes
🟢 EA 229 – Loss of flame signal
This means the boiler tried to light but couldn’t detect a stable flame.
Possible cause: A faulty ignition electrode, dirty flame sensor, or low gas pressure.
What to do: Try resetting the boiler once. If the code returns, it's best to get it checked by a Gas Safe engineer — we’ll diagnose it safely and get you back up and running.
🟢 C6 216 – Fan running too slowly
The fan isn’t working fast enough to safely push out the combustion gases.
Possible cause: Blocked flue, faulty fan, or wiring issue.
What to do: Don’t ignore this — if the boiler can’t vent properly, it shuts down for safety. Call us for a same-day inspection if needed.
🟢 A7 217 – Flow temperature sensor fault
The fan isn’t working fast enough to safely push out the combustion gases.
Possible cause: Blocked flue, faulty fan, or wiring issue.
What to do: Don’t ignore this — if the boiler can’t vent properly, it shuts down for safety. Call us for a same-day inspection if needed.
🟢 D5 – Hot water temperature sensor fault
This fault means the boiler is detecting an issue with how it heats your hot water.
Possible cause: A failing sensor or scale build-up inside the heat exchanger.
What to do: If your hot water is running cold or going hot and cold, we can flush the system or replace the sensor.
🔧 Worcester Bosch Greenstar CDi Classic (e.g., 34CDi, 38CDi)
🟢 EA – Ignition failure
The boiler couldn’t ignite successfully.
Possible cause: No gas supply, faulty ignition leads, or worn electrodes.
What to do: If you've run out of gas or had a meter change, check that first. Otherwise, don’t keep resetting it — give us a call and we’ll test the ignition system properly.
🟢 A1 – Pump overrun or airlock
The boiler pump is either stuck running too long or blocked by air.
Possible cause: Air trapped in the system, blocked pump, or pump failure.
What to do: Bleed your radiators and check the pressure. If the issue continues, we can check the pump and remove any airlocks.
🟢 C7 – Fan not running
The fan has stopped working, so the boiler can’t run safely.
Possible cause: Faulty fan motor, wiring issue, or a failed PCB.
What to do: This isn’t something you can fix yourself — we’ll need to run diagnostic checks to pinpoint the issue.
🟢 E9 – Overheat detected
Your boiler is overheating and shutting down to protect itself.
Possible cause: Pump failure, blocked pipework, or a clogged heat exchanger.
What to do: Switch the boiler off and let it cool. If this happens more than once, it’s time to book a service — we’ll flush the system if needed and check the pump.
🔧 Worcester Bosch Greenstar 4000 Fault Codes
🟢 EA 227 – Failed to ignite
The boiler has failed to light properly.
Possible cause: No gas supply, blocked burner, or ignition issue.
What to do: Try pressing reset once. If it doesn’t ignite, check your gas supply (if safe), and give us a call — we’ll get to the bottom of it.
🟢 C6 219 – Fan blocked or faulty
The fan isn’t spinning as it should, so the boiler can’t run safely.
Possible cause: Blocked flue, debris in the fan, or a failed motor.
What to do: Turn the boiler off and don’t force a reset. This fault usually needs parts tested — we’ll inspect the fan unit and flue system properly.
🟢 A1 281 – Circulation error
The boiler isn’t pushing hot water around the system effectively.
Possible cause: Pump jammed, airlock, or sludge blocking the flow.
What to do: Try bleeding radiators and check pressure. If the problem returns, we can flush the system and check the pump.
🔧 Worcester Bosch Greenstar Highflow Fault Codes
🟢 E9 219 – Overheat condition
Your boiler is overheating and has shut down to protect itself.
Possible cause: Pump failure, restricted flow, or sludge buildup in the system.
What to do: Don’t keep resetting the boiler let it cool down and give us a ring. We’ll check the pump and circulation and get things flowing properly again.
🟢 EA 227 – No flame detected
The boiler attempted to ignite but couldn’t detect a flame.
Possible cause: A gas valve issue or faulty ignition.
What to do: This fault needs a Gas Safe engineer to test safely. Contact us and we’ll check the gas pressure, ignition leads, and burner.
🟢 C6 215 – Fan error
The fan isn’t spinning fast enough, or not at all.
Possible cause: Faulty fan motor, seized bearings, or a blockage in the flue.
What to do: The boiler’s fan is crucial for safe operation. Call us to inspect and repair before restarting.
Our Worcester Bosch Boiler Installations Around Tunbridge Wells
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Speak to it Worcester accredited engineer
Still stuck or unsure what to do? We’re Worcester Accredited Installers with 30 years of experience fixing these systems. Whether it’s a one-off fault or something more serious, we’ll give you honest advice and fast support.