Worcester Boiler Error Codes, Fault Codes Meanings & Fixes

Worcester Bosch Boiler Error Codes 2026 | Causes, Fixes & Full Guide

Quick Answer: Worcester Bosch boilers display alphanumeric fault codes on their LCD screen when a problem is detected. The most common codes are EA 227 (no flame detected — often a frozen condensate pipe, DIY fix), 1017/CE 207 (low water pressure — DIY repressurise), and C6 (fan fault — Gas Safe engineer required). Always call a Gas Safe registered engineer for ignition, sensor, PCB, and gas valve faults. Never reset a boiler displaying an EA error code without first identifying the cause.

Worcester Bosch is the UK’s best-selling boiler brand, and the Greenstar range consistently achieves Which? Best Buy status. Like all mechanical heating systems, even the most reliable Worcester boiler will occasionally display a fault code. This guide covers every Worcester Bosch error code across the Greenstar 4000, 8000, CDi Compact, CDi Classic, CDi Highflow, Greenstar i, Ri, Heatslave, and GB162 ranges — with plain-English explanations of what each code means, what causes it, and whether it can be resolved without a Gas Safe engineer.

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Understanding Worcester Bosch Error Code Types

Worcester Bosch categorises its fault codes into five distinct types. Knowing which type is being displayed tells you immediately how serious the situation is and whether the boiler can still operate.

Blocking errors cause the boiler to stop operating immediately, but the fault code is not shown on the display. Press the spanner/return button to access the cause code in the information menu. Once the underlying issue is resolved, the boiler restarts automatically.

Locking errors display the fault code and cause code on screen alongside a flashing warning triangle. The boiler will not restart until the fault has been fixed and the reset button has been held for 3 seconds to clear the codes.

Fault codes are alphanumeric codes that identify the fault group and appear directly on the boiler display.

Cause codes are three-digit numbers found in the information menu, accessed via the spanner/return button. On locking errors they appear alongside the fault code. On all other fault types they are only visible in the information menu.

Maintenance codes begin with the letter H followed by a number. The boiler continues to operate when a maintenance code is displayed, but the code indicates that a qualified engineer should inspect the boiler. Ignoring maintenance codes risks a minor issue developing into a more costly fault.

How to Reset a Worcester Bosch Boiler

Depending on the model, there are two reset methods. Some models have a dedicated reset button — press and hold it for 3 seconds. On other models, turn the temperature dial fully anticlockwise until it reaches the reset symbol, hold for 3 seconds, then return the dial to the desired temperature setting.

Never reset a Worcester Bosch boiler displaying an EA error code without first identifying the cause. EA indicates no flame is detected — resetting without resolving the cause of ignition failure can cause further damage to the boiler.

Most Common Worcester Bosch Fault Codes

EA 227 — No Flame Detected (Most Common)

EA is the most frequently reported Worcester Bosch fault code. It means the boiler attempted to ignite but no flame was detected — or the flame signal was lost during operation. In cold weather, the most common cause is a frozen condensate pipe rather than an ignition fault. The condensate pipe carries acidic wastewater from the boiler to an external drain and is exposed to freezing temperatures outside. For those who encounter issues with their Worcester Bosch systems, understanding Worcester C6 fault code meanings can be invaluable. This code typically indicates a water pressure or flow issue, which can lead to improper boiler operation. Regular maintenance and monitoring can help prevent these fault codes from occurring and ensure the system runs efficiently.

To check for a frozen condensate pipe, locate the white plastic pipe that exits the boiler and runs to an external drain. If the pipe is frozen, pour warm — not boiling — water along its length until the blockage clears. Reset the boiler after thawing. If EA 227 persists after the condensate pipe is confirmed clear, or if the weather is not cold enough for freezing to be the cause, a Gas Safe engineer should investigate the ignition electrode, flame sensor, and gas supply.

DIY action: Check and thaw condensate pipe in cold weather. Check that the gas supply isolation valve is open. Engineer required: Faulty ignition electrode, damaged ionisation cable, gas supply fault, burner control unit failure.

1017 / CE 207 — Low Water Pressure

Low water pressure prevents the boiler from operating correctly and is one of the most commonly resolved faults without an engineer visit. The boiler requires system pressure between 1.0 and 1.5 bar to function. When pressure drops below this threshold, the fault code is displayed and heating stops.

To resolve, locate the filling loop — a flexible braided hose connected to the pipework beneath the boiler — and open the valve or valves slowly until the pressure gauge reads 1.5 bar, then close the loop. Reset the boiler. If pressure drops again within a short period, a system leak is the likely cause and a Gas Safe engineer should investigate.

DIY action: Repressurise via the filling loop to 1.5 bar. Engineer required: Pressure drops repeatedly, indicating a system leak.

C6 / C6 215/216 — Fan Fault

The fan ensures combustion gases vent safely through the flue. A C6 code indicates the fan speed is outside its acceptable range — either too fast or too slow. In some cases this is linked to a frozen or blocked condensate pipe causing back pressure, so checking and clearing the condensate pipe is worth attempting first. If the condensate pipe is clear and C6 persists, the fan, wiring harness, or control board requires inspection by a Gas Safe engineer.

DIY action: Check and clear the condensate pipe. Engineer required: Fan replacement, wiring harness check, control board inspection.

A21 — Thermostat Communication Error (RF Signal Lost)

The A21 code means the boiler and wireless thermostat have lost their RF communication signal. This is one of the few fault codes that can often be resolved without an engineer. Check that the thermostat has working batteries and that nothing has been placed between the thermostat and the boiler receiver that could block the signal — such as a new appliance or furniture rearrangement. Re-pairing the thermostat to the receiver following the manufacturer’s instructions usually clears A21 without any further action.

DIY action: Check thermostat batteries, remove signal obstructions, re-pair thermostat to receiver. Engineer required: If signal cannot be restored after re-pairing.

E9 / E9 219/224 — Safety Temperature Limiter Tripped

E9 indicates the safety temperature limiter has activated because the boiler has reached an unsafe temperature. This is a safety lockout that should not be manually cleared without establishing the cause. Common causes include a faulty pump preventing water circulation, a blocked heat exchanger, or a stuck zone valve. A Gas Safe engineer is required to identify and resolve the root cause before the boiler is restarted.

DIY action: None — do not reset until cause is established. Engineer required: Always — pump fault, heat exchanger blockage, zone valve, or sensor fault.

F7 / FA — False Flame Detected

F7 means a flame signal is being detected before the burner has started, and FA means a flame signal is present after the gas valve has closed. Both indicate a potentially serious fault — either the ionisation electrode is faulty or, more critically, the gas valve is not closing fully. FA in particular should be treated as a safety concern requiring prompt engineer attendance. Do not reset repeatedly if these codes appear.

DIY action: None. Engineer required: Always — ionisation electrode or gas valve replacement required.

Worcester Greenstar 8000 Error Codes

Worcester Greenstar 4000 Error Codes

Worcester Greenstar CDi Compact Error Codes

Worcester Greenstar CDi Highflow Error Codes

Worcester Greenstar CDi Classic Regular Error Codes

Worcester Greenstar i Combi and System Error Codes

Worcester Greenstar Heatslave Error Codes

Worcester Greenstar Ri Error Codes

Worcester GB162 Error Codes

DIY vs Engineer: Quick Reference

FAQ

What is the most common Worcester Bosch error code?

EA 227 is the most frequently reported Worcester Bosch error code. In cold weather it almost always indicates a frozen condensate pipe, which is a straightforward DIY fix — thaw the external pipe with warm water and reset the boiler. If EA 227 appears in mild weather, or returns after the condensate pipe has been cleared, a Gas Safe engineer should investigate the ignition electrode, flame sensor, or gas supply.

Can I reset my Worcester Bosch boiler myself?

Yes, for most fault codes. Press and hold the reset button for 3 seconds, or turn the temperature dial to the reset position and hold for 3 seconds depending on the model. The exception is an EA error code — never reset a Worcester boiler showing EA without first identifying and resolving the cause, as repeated reset attempts without fixing the underlying fault can cause further damage.

What does a flashing blue light on a Worcester boiler mean?

A flashing blue light on a Worcester Bosch boiler typically accompanies an EA fault code, indicating that the boiler is attempting to detect a flame but failing. The most common cause in cold weather is a frozen condensate pipe. Check and thaw the external condensate pipe before contacting a Gas Safe engineer if the fault persists.

How do I fix low pressure on a Worcester Bosch boiler?

Low pressure on a Worcester Bosch boiler — indicated by fault codes 1017, CE 207, or H07 — is resolved by repressurising the system via the filling loop. Locate the filling loop beneath the boiler, open the valve or valves slowly, and watch the pressure gauge rise to 1.5 bar, then close the loop and reset the boiler. If pressure drops again within days or weeks, a system leak requires investigation by a Gas Safe engineer.

What does the H code mean on a Worcester Bosch boiler?

H codes are maintenance codes — the boiler continues to operate when one is displayed but the code indicates that a qualified engineer should inspect the unit. H07 is the most common, indicating low water pressure. H27 and H29 indicate sensor faults on the GB162 and Heatslave ranges respectively. Maintenance codes should not be ignored, as the underlying issue will typically worsen over time.

When should I call a Gas Safe engineer for a Worcester boiler fault?

Call a Gas Safe engineer for any fault code involving ignition failure that persists after the condensate pipe has been checked, any E9 safety temperature lockout, any F7 or FA false flame code, any F0 internal or PCB error, any fan fault (C6 or C7) that is not resolved by clearing the condensate pipe, any sensor fault, and any gas valve fault. If in doubt, always call an engineer — attempting DIY repairs on a gas boiler is illegal without Gas Safe registration and risks both safety and warranty validity.

Conclusion

Worcester Bosch’s comprehensive fault code system makes diagnosis more straightforward than most boiler brands, with cause codes in the information menu providing additional detail beyond the primary fault display. For the majority of homeowners, the most likely codes encountered — EA 227 frozen condensate in winter and low pressure requiring repressurisation — are both straightforward to resolve without calling an engineer. All other fault codes, particularly E9 safety lockouts and F7/FA false flame codes, require a Gas Safe registered engineer and should not be cleared by repeated resetting. When facing issues identified by Worcester U9 fault code solutions, it’s important to follow the manufacturer’s guidance for troubleshooting. Homeowners should familiarize themselves with common resolutions listed in the manual to tackle minor errors effectively. In more complex situations, timely assistance from a qualified technician can ensure the boiler operates safely and efficiently.

An annual Worcester Bosch service is the most effective way to prevent fault codes from appearing in the first place — the manufacturer requires it to maintain warranty validity, and it is the point at which developing faults are identified and resolved before they trigger a lockout.