Worcester Bosch error codes

The most common Worcester Bosch fault codes

Common Worcester Bosch Boiler Error Codes

In this guide, we are going to highlight the most common Worcester BOSCH error codes that can show up on your boiler and explain what they mean so you can solve any issues yourself at home.


Things to Consider if you have a Worcester Bosch error code:

Before you begin to stress and worry about being out of pocket when a code appears on your Worcester Bosch Greenstar boiler, there are three things you should consider first:

Is Your Boiler Still Covered?

Worcester is renowned for having long warranties on their boilers, so the first thing to do whenever an issue arises is to check whether you are still covered.

In some cases, your boiler might be backed by a ten-year warranty which can make it cheaper to have any issues resolved by a professional.

Check your warranty length using Worcester Bosch online guarantee checker

Have You Reset The Boiler?

We have all heard the classic ‘turn it off and on again’ as a solution for when things go wrong, but there is some truth behind the cliché.

In some cases, an error code might show even if there is not a mechanical problem so to save yourself time and effort try turning the device off to see whether it goes away.

If the error code appears once the boiler has rebooted, it is time to look further into it.

Any worcester Boiler installed since 2019 will have the error name rather then an error code.

Have you checked the pressure?

Low pressure is a sign that there isnt enough water in your system, Check for leaks and top up using the filling loop. This can be located on your boiler or externally underneath your boiler. Occasionally it is located else where around the house. Consult your installation instructions on advice on how to do this.

Common Worcester BOSCH Error Codes

The following fault codes can appear on a Worcester BOSCH Greenstar boiler for various reasons:

Fan Speed Error: C6 215

This fault code indicates that the fan speed in your Worcester Greenstar boiler is too high.

The fan speed might return back to normal once you have restarted the boiler, if not it needs checking by a boiler engineer.

Heat Control Module (HCM) Issues: 9A 362

This indicates that the control box or the Heat Control Module (HCM) is defective on your Worcester BOSCH. A fault code indicating that the heat control module (HCM) is defective on your boiler, could also be a sign that the incorrect HCM fitted 9U.

When you see the fault codes for the Heat Control Module (HCM) is defective an engineer needs to be called to check your Worcester BOSCH boiler as it may need replacing.

No Flame Signal Due To Blockage or Internal Leak: EA 227

When this code appears on the control box of your Worcester boiler, it can mean several different things. This code indicates an issue with the gas valve, as no flame can be found.

This can indicate that the gas valve may need replacing, but it can also be a sign that the gas ratio control valve needs adjusting which you can do yourself.

This fault code can also indicate that the condensate discharge pipe is blocked or frozen, in which airflow stopped during operation. This can cause the flue gas thermostat overheat and needs to be solved quickly.

This code can be a sign that the operation is defective. Check the connecting lead as it might show that the electrode or ignition lead has been damaged, which will prevent a flame signal.

These are not issues you can handle yourself if they appear on your combi boiler. The codes fault will need to be solved by a boiler engineer or through getting a new boiler if you are no longer under warranty.

Another reason could be due to a frozen condensate pipe

Blocked Pump: A1 281

When this code appears, it means that the pump stuck or running with air in the system, which is an internal error. This can cause air-gas ratio control issues in the Worcester boiler.

Turning the box or heat control reset button can solve this issue in your combi boiler.

If turning the control box or heat on and off again does not solve the issue, an engineer will need to be called.

Minimum Burner Load: EF 349

This means the primary flow is operating at minimum burner level. Once this is detected, check the safety temperature valve is between 1 and 1.5 pulses, check service mode on the burner control unit if this is the case.

The temperature sensor may need replacing.

Flow Temperature High: No Code 212

This indicates that the flow temperature too high and will need checking to return temperature back to the normal state.

This can indicate that the safety temperature limiter has tripped and needs replacing.

To restart the temperature flow sensor short circuit, turn the boiler off and on again to trigger the low mains voltage. This should reset the high limit thermostat activated code and prevent the gas thermostat overheat EA codes fault to appear.

Loss Of Ionisation Detected: Worcester bosch error code EA 229

This shows that there is a loss of ionisation signal detected before burner start or during operation.

If the temperature sensor correctly installed, the pressure should be between 1.0 and 1.5 bars. Connections need checking, and the boiler should be reset if ionisation detected after ignition to resolve the issue.

Flow Temperature Sensor Too High: Worcester bosch error code E5 218

If the flow temperature sensor or hot water temperature sensor on the burner control unit is too high, these boiler error codes will appear.

This is not something that you can change in the control box, if the temperature sensor is defective, it will need to be replaced.

Sensor Too High: Worcester bosch error code 2964 B

The signal from the heat exchanger temperature sensor is out of range for the primary flow temperature.

The safety or flow temperature can be reset by turning the modulating gas valve anticlockwise to trigger a reset position.

Low Water Pressure: Worcester bosch error code 1017 W

This can be a sign that the water needs topping up in your Worcester boiler. If you are having issues with domestic hot water, then the vent system or pressure sensor may need to be replaced.

If the boiler is not under warranty, it may be easier to buy a new boiler.

Safety Sensor Code 226

This means that a safety sensor has been connected to the blocking error history menu, which can be resolved by restarting the boiler.

If this code does not go away, the boiler may no longer be gas safe, and you will need to buy a new boiler.

Worcester Bosch Error codes – Flashing lights

In some cases, the light on your central heating control box or the heat control module can flash to indicate that connections need checking.

A slow flash mostly on a Worcester BOSCH control box that goes for two pulses can indicate that you need to check service mode switch as it is in the minimum position.

A fast flash will indicate that the code plug is blocked.

To deal with a code plug block, reset the boiler by turning the control knob anticlockwise. This can restart your central heating system.


Sometimes, Worcester Bosch boiler error codes indicate a small problem that can be solved at home. However, it is always a good idea to get an engineer to check your handywork.


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