Worcester Bosch Boiler Fault Codes: Complete Guide
If you notice unusual letters and numbers flashing on your Worcester Bosch boiler, you are not alone. These boiler fault codes are intended to assist in detecting problems quickly, saving time, money, and stress.
In this detailed guide, we’ll go over the most frequent Worcester Bosch boiler fault codes, explain what they mean, and recommend solutions on how to fix or respond to each one.
List of Common Worcester Bosch Boiler Fault Codes (With Fixes)
| Error Code | Issue | Meaning |
| 9A 362 | Incorrect HCM Fitted | The incorrect Heat Control Module (HCM) was installed. |
| 9U 233 | Heat Control Module (HCM) Error | Code plug issue or HCM fault. |
| B7 257 | Internal Error | Control board issue. |
| C6 215 | Fan Problem | The fan is running too fast. |
| D1 240 | Return Sensor Error | A sensor may be wet or damaged. |
| E2 222 | Flow Sensor Short Circuit | Electrical fault in the flow sensor. |
| E5 218 | Flow Temperature Too High | Overheating in the flow pipe. |
| E9 219 | Safety Sensor Fault | The temperature is too high, sensor issue. |
| E9 220 | Safety Sensor Short Circuit | Max temp sensor failure. |
| E9 221 | Safety Sensor Open Circuit | The sensor is not recognized by the boiler. |
| E9 224 | Max Temperature Thermostat Activated | Flue gas overheat detected. |
| EA 229 | Loss of Flame Signal | Established flame extinguished. |
| EA 234 | Gas Valve Error | Gas valve coil disconnected. |
| EA 261 | Ignition Timing Error | No flame detected in the ignition window. |
| EA 338 | Too Many Short Burner Starts | The pump is not detecting water. |
| A1 281 | Pump Stuck or Air in System | Little or no water circulation. |
| C1 264 | Airflow Stopped | The fan stopped working. |
| EF 349 | Central Heating Boil Detected | The flow and return temperature difference is too high. |
| NO CODE 212 | Safety or Flow Temperature Rising Too Fast | Airlock or low water content in the system. |
Here is a detailed breakdown of common worcester bosch boiler codes
You can refer to this as a guide; however, if you think you cannot handle the error code or it needs immediate attention that it is always recommended to call over a gas safe engineer who can figure out the problem that your boiler is having.
9A 362 – Incorrect HCM Fitted Error
Meaning: The Heat Control Module (HCM) is not correctly matched or fitted in your Worcester Bosch Boiler.
Fix: This may require you to call a Gas Safe Engineer to inspect your boiler. They will then replace the HCM with the correct model.
9U 233 – Heat Control Module (HCM) Error
Meaning: Code plug issue in the HCM.
Fix: Requires technician support to reprogram or replace the control module.
B7 257 – Internal Error
Meaning: Likely a control board issue.
Fix: A qualified Gas Safe Engineer will need to inspect your boiler. Replacing the PCB (Printed Circuit Board) may solve the error.
C6 215 – Fan Problem
Meaning: The Fan of your boiler is running too fast.
Fix: This could indicate a sensor fault or airflow issue. Needs diagnosis by a heating Gas Safe engineer.
D1 240 – Return Sensor Error
Meaning: The Sensor may be wet, damaged, or faulty.
Fix: A gas-safe engineer may need to dry, test, or replace the return sensor.
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E2 222 – Flow Sensor Short Circuit Error
Meaning: Electrical fault in the flow sensor.
Fix: The sensor may require replacement by a Gas Safe Engineer.
E5 218 – Flow Temperature Too High
Meaning: Your Worcester Boiler water temperature is exceeding safe limits.
Fix: Check for blocked radiators or pump failure. The system may need bleeding.
E9 Series – Safety Sensor & Temperature Faults
E9 219 – Safety Sensor Fault
Cause: Excessive temperature or sensor malfunction can cause your boiler to show this error code.
Fix: Professional sensor testing and boiler inspection are needed.
E9 220 – Safety Sensor Short Circuit
Cause: Main heat exchanger temperature sensor failure.
Fix: Replace the sensor.
E9 221 – Safety Sensor Open Circuit
Cause: Sensor not recognised.
Fix: Could be a wiring or sensor failure—requires technician support.
E9 224 – Max Temperature Thermostat Activated
Cause: Flue gas thermostat overheated.
Fix: Likely due to poor airflow—clean flue, inspect fan, or replace sensor.
EA Series – Ignition and Flame Detection Faults
EA 229 – Loss of Flame Signal During Operation
Cause: Flame extinguished due to moisture or a blocked sump/condensate trap.
Fix: Clean the condensate trap and inspect for water ingress.
EA 234 – Gas Valve Error
Cause: Gas valve coil disconnected.
Fix: Needs an engineer to reconnect or replace the valve.
EA 261 – Ignition Timing Error
Cause: No flame was established during the ignition period.
Fix: May involve adjusting ignition settings or replacing the igniter.
EA 338 – Too Many Short Burner Starts
Cause: The Pump may not detect water.
Fix: Check the pressure gauge; repressurise your boiler to 1 bar.
A1 281 – Pump Stuck or Air in System
Meaning: This error can show up on your Worcester Bosch Boiler because of circulation issue due to low water pressure or airlock.
Fix: Repressurise your boiler to 1 bar and bleed radiators.
C1 264 – Airflow Stopped During Operation
Meaning: The Fan has stopped working.
Fix: The error could be due to blockage or a faulty fan. You need to call a Gas Safe engineer for inspection.
EF 349 – Central Heating Boil Detected
Meaning: Temperature difference between flow and return > 18°C.
Fix: Might be caused by poor circulation, pump fault, or system blockage. You have to contact a Gas Safe engineer to fix the issue.
No Code 212 – Safety or Flow Temperature Rising Too Fast
Meaning: Airlock or insufficient water in the system.
Fix: Check the pressure gauge, top up pressure, and bleed air from the system.
When to Contact a Gas Safe Engineer
Some fixes, such as repressurising or resetting, are easy and DIY-friendly.
However, many Worcester Bosch error codes are caused by gas, electrical, or complicated mechanical defects.
Errors such as EA 234 (Gas Valve Error), E9 224 (Max Temperature Thermostat), and B7 257 (Internal Error) require professional intervention to assure safety and regulatory compliance.
Need professional boiler repair service? Contact a Gas Safe engineer from PlusHeat today.
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