Worcester Bosch Boiler Error Codes

By using the table below, you can find information about the most common Worcester Bosch boiler fault codes and information on how to diagnose and solve the issue. The error codes below relate to the Worcester Bosch’s CDI and Greenstar models. Be sure to check your model's manual for further information.


Error CodeFault Name & Description

Safety Temperature Limiter has tripped.

 The boiler has detected an issue with its temperature and has safely shut down. The part of the boiler causing the issue will depend on the error code that follows the E9 code:

  • E9 219 – this is a heat exchanger fault, so the boiler has detected a temperature on the heat exchanger over 105°C. This means that the heat exchanger is faulty.
  • E9 220 - the same as 219, the heat exchanger temperature has been detected as too high. However, a 220 fault means that the issue is with the temperature sensor, not the heat exchanger itself.
  • E9 221 –the boiler cannot recognise or read the temperature sensor. This suggests a fault with the wiring, the connection of the sensor, or the PCB itself.
  • E9 224 –excessive temperatures have been detected in the flue gases leaving the boiler. This can be caused by a range of different factors, most commonly it means there is a blockage somewhere in the boiler or heating system.
Error CodeFault Name & Description

Flame not detected.

 This means that the boiler cannot detect a flame after ignition, so it has shut down safely until the problem is rectified. This can be caused by a number of issues:

  • Gas flow problems – if the boiler is not receiving enough mains gas, or the pressure is too low, then it will be unable to light.
  • Condensate pipe issues – if the condensate pipe is blocked or frozen, the boiler will be unable to light.
  • Sensor or electronic fault that is causing the boiler to fail to detect the flame.
Error CodeFault Name & Description

“False Flame” - flame detected when boiler was shut off.

 This fault means that the boiler has detected a flame when there should not be one because the boiler is either off or on standby. Upon detecting the flame, the boiler will shut down for safety. This can occur for a number of different reasons:

  • Ignition electrodes could be faulty, damaged, or dirty.
  • There could be a problem with the flue.
  • This could also be an electrical fault with the sensor, or a problem with the boiler’s PCB.