Worcester Bosch E9 Fault code

Worcester Bosch E9 Fault code

The Worcester Bosch E9 fault code is a significant error indicating an issue with the boiler’s temperature getting too high. This overheating problem can be a result of several underlying causes and requires immediate attention to prevent damage to the boiler and ensure safety. Here’s a detailed look at what the E9 fault code means, potential causes, and steps for resolution:

Causes of the E9 Fault Code

  1. Pump Failure: The circulation pump plays a crucial role in moving hot water through the system and preventing the boiler from overheating. If the pump fails or operates inefficiently, it can lead to an increase in temperature, triggering the E9 fault.
  2. Blocked System: Blockages in the pipes or heat exchanger can restrict water flow, causing the water to overheat. Sludge buildup or debris in the system is a common cause of such blockages.
  3. Faulty Thermistor: Thermistors measure the water temperature in the boiler. A faulty thermistor might incorrectly read the temperature, causing the boiler to overheat or the system to think it’s overheating when it’s not.
  4. Pressure Issues: Incorrect system pressure, whether too high or too low, can affect the boiler’s ability to circulate water properly, potentially leading to overheating.
  5. Faulty PCB: The Printed Circuit Board (PCB) controls the boiler’s operations, including temperature regulation. A malfunctioning PCB can mismanage the heating process, resulting in excessive temperatures.

Troubleshooting and Resolving the E9 Fault Code

  1. Reset the Boiler: Initially, try resetting the boiler to see if the fault clears. However, if the E9 code persists, further investigation is needed.
  2. Check the Pump: Ensure that the pump is working correctly. Listen for unusual noises that might indicate a failure or obstruction. A Gas Safe registered engineer can assess and replace the pump if necessary.
  3. Inspect for Blockages: Look for any signs of blockage in the system. This may involve checking the pipes and heat exchanger for sludge or debris. A professional heating engineer can perform a system flush to clear any blockages.
  4. Evaluate the Thermistor: Test the thermistor to ensure it’s providing accurate temperature readings. Faulty thermistors should be replaced by a qualified technician.
  5. Assess System Pressure: Check the boiler’s pressure gauge to ensure the pressure is within the recommended range. Adjust the pressure if it’s too high or too low, following the manufacturer’s guidelines.
  6. Examine the PCB: If other causes have been ruled out, the PCB might be at fault. PCB replacement is a complex process that should only be carried out by a professional.


The E9 fault code on a Worcester Bosch boiler indicates a serious overheating issue that requires prompt attention. Due to the potential complexity of the underlying causes, it’s advisable to contact a Gas Safe registered engineer to diagnose and resolve the problem safely. Regular maintenance and servicing can help prevent such faults by ensuring the boiler and its components are in good working order.