Common Worcester Bosch Boiler Error Codes

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What is a Boiler Error Code?

A boiler error code is an alphanumeric indication displayed on your boiler's control panel. These codes are used by manufacturers to help identify specific issues or faults within the boiler system.

Each code corresponds to a particular problem, such as pressure loss, ignition failure, or overheating. By understanding these codes, homeowners can diagnose issues more efficiently and determine whether they can be resolved through simple troubleshooting or require professional attention.

Things to Consider

Before you begin to stress and worry about being out of pocket when a code appears on your Worcester Bosch Greenstar boiler, there are two 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.

Worcester Bosch is one of the most reputable names in the UK heating market, but it’s not the only reliable brand out there. Take a look at our expert guide to the best boiler brands to see how other leading manufacturers like Vaillant, Viessmann and Alpha compare in performance, warranty, and value.

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.

However, if your boiler is out of warranty or you’re facing frequent repair costs, it may be time to compare prices for a replacement. Our 2025 new boiler cost guide explains what to expect when budgeting for a new installation, including typical prices for combi, system, and regular boilers.

When to Call a Gas Safe Engineer?

It is crucial to call a Gas Safe registered engineer if you encounter persistent or serious boiler issues indicated by error codes, such as frequent ignition failures, repeated pressure drops, or overheating.

Additionally, if you smell gas, see signs of carbon monoxide leaks, or if the boiler displays unfamiliar or complex error codes, professional intervention is necessary. Gas Safe engineers are certified to handle gas appliances safely and can ensure that your boiler is repaired correctly and efficiently, maintaining both your safety and the boiler's performance.

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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.

Common Worcester BOSCH Error Codes

Comprehensive Guide to Worcester Bosch Boiler Error Codes

Welcome to iHeat’s ultimate guide to understanding and troubleshooting Worcester Bosch boiler error codes.

If your existing Worcester Bosch combi is showing frequent errors and nearing the end of its lifespan, you may be considering an upgrade. Check out our 2025 list of the best combi boilers to discover efficient, compact models suitable for homes of every size.

Worcester BOSCH Error Code A1

• Meaning: Low water pressure.

• Causes: Leak in the system, pressure relief valve issue, or recent bleeding of radiators.

• Solutions: Repressurize the system to 1-1.5 bar. Inspect for visible leaks and repair them. Check the pressure relief valve for proper functioning.

Worcester BOSCH Error Code C6

• Meaning: Fan speed too low.

• Causes: Blocked flue, fan motor issue, or control board problem.

• Solutions: Ensure the flue is clear of blockages. Check and replace the fan motor if necessary. Test the control board and replace it if needed.

Worcester BOSCH Error Code E9

• Meaning: Overheat lockout.

• Causes: Faulty pump, airlock in the system, or thermostat failure.

• Solutions: Verify the pump operation and replace it if faulty. Bleed the system to remove any airlocks. Check the thermostat and replace it if necessary.

Worcester BOSCH Error Code EA

• Meaning: Ignition failed.

• Causes: Gas supply issue, ignition electrode fault, or flue gas sensor issue.

• Solutions: Ensure the gas supply is turned on and the meter is functioning. Inspect and clean the ignition electrode. Verify the flue is not blocked.

Worcester BOSCH Error Code D1

• Meaning: Sensor fault.

• Causes: Faulty NTC thermistor, wiring issue, or control board fault.

• Solutions: Check and replace the NTC thermistor. Inspect the wiring for any issues. Test and replace the control board if necessary.

Worcester BOSCH Error Code A7

• Meaning: Hot water NTC sensor fault.

• Causes: Faulty sensor, wiring issue, or connection problem.

• Solutions: Replace the hot water NTC sensor. Inspect wiring and secure connections.

Worcester BOSCH Error Code B7

• Meaning: Hot water outlet sensor short circuit.

• Causes: Faulty sensor, wiring issue, or connection problem.

• Solutions: Replace the hot water outlet sensor. Inspect wiring and secure connections.

Worcester BOSCH Error Code 9A

• Meaning: Coding card not recognised.

• Causes: Incorrect coding card, card not inserted correctly, or faulty control board.

• Solutions: Verify and replace the coding card if necessary. Ensure proper insertion. Test and replace the control board if needed.

Worcester BOSCH Error Code 297

• Meaning: Burner control fault.

• Causes: Burner issue, gas valve fault, or control board problem.

• Solutions: Inspect the burner and clean or repair it. Check and replace the gas valve. Test and replace the control board if necessary.

Worcester BOSCH Error Code 385

• Meaning: Safety temperature limiter.

• Causes: Overheating, faulty safety temperature limiter, or circulation issue.

• Solutions: Allow the boiler to cool down. Replace the safety temperature limiter. Ensure proper circulation by checking the pump and system pressure.

Worcester BOSCH Error Code F0

• Meaning: No heating demand from external controls.

• Causes: Faulty external controls or wiring issue.

• Solutions: Inspect and repair external controls. Check wiring connections.

Worcester BOSCH Error Code F1

• Meaning: Return sensor fault.

• Causes: Faulty sensor or wiring issue.

• Solutions: Replace the return sensor. Inspect wiring and secure connections.

Worcester BOSCH Error Code F7

• Meaning: Flow sensor fault.

• Causes: Faulty sensor or wiring issue.

• Solutions: Replace the flow sensor. Inspect wiring and secure connections.

Worcester BOSCH Error Code F8

• Meaning: Flow temperature sensor fault.

• Causes: Faulty sensor or wiring issue.

• Solutions: Replace the flow temperature sensor. Inspect wiring and secure connections.

Worcester BOSCH Error Code F9

• Meaning: Water pressure sensor fault.

• Causes: Faulty sensor or wiring issue.

• Solutions: Replace the water pressure sensor. Inspect wiring and secure connections.

Worcester BOSCH Error Code A8

• Meaning: Condensate pump fault.

• Causes: Faulty condensate pump or blocked pipe.

• Solutions: Check and replace the condensate pump if necessary. Clear any blockages in the pipe.