If your Worcester Bosch boiler display is showing an error code, it’s indicating a specific issue within the system. While some minor problems might have simple solutions you can safely check, many Worcester Bosch error codes point to internal faults that require the expertise of a Gas Safe registered engineer.
⚠️ IMPORTANT SAFETY WARNING: Working with gas appliances can be extremely dangerous and should ONLY be undertaken by a qualified, Gas Safe registered engineer. The information below is for general guidance. NEVER attempt to open your boiler or perform complex repairs yourself. If you smell gas, suspect a leak, or are unsure, turn off your gas supply and call a Gas Safe engineer immediately.
Common Worcester Bosch Boiler Fault Codes:
Here are some of the most frequently encountered Worcester Bosch error codes:
1. EA 227 – No Flame Detected / Ignition Fault
This is one of the most common Worcester Bosch fault codes. It means the boiler attempted to ignite but failed to detect a flame, leading to a safety lockout.
No gas supply (e.g., gas meter valve closed, low gas pressure in the area, pre-payment meter out of credit).
Frozen or blocked condensate pipe (especially in cold weather).
Faulty ignition electrode or lead.
Faulty gas valve.
Air in the gas supply.
Ensure your gas supply is on and other gas appliances (like your hob) are working.
If you have a pre-payment meter, check your credit.
Check for a frozen condensate pipe outside your property (a white/grey plastic pipe, often near a drain). If frozen, you may be able to gently thaw it with warm (not boiling) water, then reset the boiler.
If these simple checks don’t resolve the EA 227 code, it’s likely an internal gas supply, ignition, or component fault that requires a Gas Safe registered engineer.
2. A1 – Low Water Pressure / Circulation Fault
This code often indicates low water pressure in the heating system or a problem with water circulation.
System leak (even a small one can cause pressure drops over time).
Recently bled radiators (releasing air also releases some water).
Faulty pump or airlock in the pump.
Problem with the pressure relief valve.
Check the pressure gauge on your boiler; it should typically be between 1 and 1.5 bar when the system is cold.
If the pressure is low, you can re-pressurise the system using the internal filling loop, following your Worcester Bosch boiler’s specific manual instructions carefully.
Check radiators for any obvious leaks or cold spots (indicating air).
If the pressure drops frequently after topping up, or if you suspect a leak or pump issue, a professional diagnosis is needed.
3. C6 – Fan Fault
This code indicates an issue with the boiler’s fan, which is crucial for expelling combustion gases and drawing in fresh air. The fan speed is likely outside its expected operating range.
Faulty or seized fan motor.
Blockage in the flue or air intake.
Problem with the air pressure switch.
Wiring issues to the fan.
Visually inspect the flue terminal outside your property for any obvious obstructions (e.g., bird’s nest, debris).
A C6 fault is a safety-critical issue related to flue gases. Do not attempt to fix this yourself. A Gas Safe registered engineer must diagnose and repair the fan or related components.
4. E9 – Overheating / Safety Temperature Limiter Tripped
The boiler has detected that its internal temperature has exceeded a safe limit and has shut down as a safety measure. This is a critical fault.
Blocked heat exchanger (due to sludge or limescale).
Faulty or blocked pump, preventing water circulation.
Faulty safety temperature limiter or sensor.
Air in the system.
Closed radiator valves or system blockages.
Ensure all radiator valves are fully open.
Check that the system pressure is adequate (1-1.5 bar).
An E9 fault is serious and requires immediate professional attention. Do not attempt to reset or restart the boiler repeatedly without professional diagnosis. A Gas Safe engineer will need to identify the cause of the overheating.
5. D1 – Return Sensor Fault
This code indicates a problem with the return temperature sensor, which monitors the temperature of the water returning to the boiler from the heating system.
Faulty NTC (Negative Temperature Coefficient) thermistor sensor itself.
Wiring issues to the sensor (loose or damaged).
Sludge or debris in the system affecting sensor readings.
You can try resetting the boiler.
Ensure radiators are bled and the system pressure is correct, as poor circulation can sometimes lead to unusual temperature readings.
If the D1 fault persists after a reset and basic checks, the sensor or its wiring likely needs professional testing or replacement.