Common Worcester Bosch boiler fault codes

Worcester Bosch boilers are known for their reliability and performance, but like all appliances, they can sometimes run into issues. Fortunately, many of the most common problems are easily diagnosed through the boiler’s fault code system.

If you’ve found a fault code flashing on your display, this guide will help you understand what it means and whether it’s something you can fix yourself – or if it’s time to call a professional.

Greenstar i Series (e.g., 25i, 30i)

EA 227 – No Flame Detected
This usually means your boiler has failed to ignite. It could be due to a temporary gas supply issue or a problem with the ignition components. If you’ve recently had a power cut or turned off your gas, try resetting the boiler once everything is back to normal.

D1 286 – Low System Pressure
Your boiler needs enough water pressure to work properly. If it drops below 1.0 bar, you may see this code. Try topping up your boiler using the filling loop – but if the pressure keeps dropping, there might be a leak somewhere in the system.

Greenstar Si Compact

C6 216 – Fan Running Slowly
The fan is essential for safely expelling combustion gases. If it runs too slowly, the boiler will shut down for safety. This might be due to a blocked flue or a failing fan motor.

A7 217 – Flow Temperature Sensor Fault
This sensor monitors how hot the water is as it flows through the system. A fault here could mean inaccurate temperature readings or inconsistent heating performance.

Greenstar CDi Classic

A1 – Pump or Circulation Error
This often means the pump is stuck or there’s air in the system preventing water from circulating. Bleeding radiators or checking the pump can sometimes help, but if the code returns, call an engineer.

E9 – Overheat Lockout
If the boiler gets too hot, it will shut down to protect itself. This could be caused by a blocked heat exchanger, pump failure, or restricted water flow.

Greenstar 4000

C6 219 – Fan Fault
If the fan isn’t spinning freely, the boiler won’t ignite. This can be caused by dirt or debris, or it might indicate a motor fault. Best to get this one checked by a professional.

A1 281 – Circulation Error
Like the CDi Classic, this can be down to a pump issue or airlock. If radiators are cold or unevenly warm, it could point to this kind of problem.

When to Call a Professional Heating Engineer

Some faults – like low pressure – are relatively simple to fix yourself. But for anything involving ignition, sensors, or internal components, it’s best to call a Gas Safe registered engineer. Never attempt to open or repair sealed boiler components yourself. Give KHS Heating a call and arrange a boiler repair!

Want to see the full list of Worcester Bosch fault codes?

Check out our dedicated boiler fault code page for a full breakdown by model and code.