A Worcester boiler fault code is the boiler telling you what has gone wrong. It is a short letter-and-number code on the display – like EA 227 or A1 281 – that points to one specific fault, anything from a frozen pipe to a failed sensor.
Here is the short version. Find your code in the tables below to see what it means. Some faults you can clear yourself in a few minutes. Anything involving gas, ignition, sensors or the PCB needs a Gas Safe engineer.
Before anything else, two quick checks fix a big share of Worcester faults: make sure the pressure gauge reads 1–1.5 bar when the boiler is cold, and if it is cold outside, look for a frozen condensate pipe.
- Content Guide
- » The Five Types of Worcester Fault Code
- » Most Common Worcester Fault Codes (and What to Do)
- » Worcester Fault Codes by Model
- » Worcester Boiler Symbols Explained
- » Basic Troubleshooting You Can Try
- » When to Call a Gas Safe Engineer
- » Preventing Worcester Boiler Faults
- » Print or Bookmark This Fault Code List
- » Worcester Boiler Repair in London
The five types of Worcester fault code
Worcester sorts every fault into one of five types. The type tells you how urgent it is.
| Fault Type | What It Means |
|---|---|
| Locking error | A major fault. The code flashes next to a warning triangle, with a fixed "cause" code beside it. The boiler will not run until it is fixed and reset. |
| Blocking error | The boiler stops but shows no code at first. Press the return/spanner button to see the cause code. Often clears once the blockage, such as a frozen condensate pipe, is sorted. |
| Fault error | A standard alphanumeric code, such as E2, pointing to a specific component or system. |
| Maintenance code | Starts with "H". The boiler keeps running, but a service is due. Book one before it turns into a breakdown. |
| Cause error | A three-digit number, such as 227 or 212, giving extra diagnostic detail. You will usually find it in the information menu. |
Most common Worcester fault codes (and what to do)
These are the codes we see most often, with what you can safely check yourself.
EA 227 – No flame detected
The boiler tried to light and could not. Usual causes are a gas supply issue, faulty ignition electrodes, or a blocked or frozen condensate pipe in cold weather.
What to check: Look for a frozen condensate pipe outside – the white plastic pipe running to a drain. Pour warm (not boiling) water over any ice to clear it. Do not keep resetting an EA code, as it can point to a gas safety issue. More detail in our EA 227 fix guide.
E9 224 – Overheat lockout
The boiler has overheated, usually from poor circulation or a pump problem. It is a safety cut-out.
What to check: Make sure all radiator valves are open and the pressure gauge reads 1–1.5 bar when cold. See our E9 224 guide for the full walk-through.
A1 281 – Pump stuck or air in the system
The pump is stuck or running dry, often from trapped air or a mechanical fault.
What to check: Listen for gurgling or banging from the boiler. That usually means air in the system that needs bleeding out.
212 – Flow temperature rising too fast (overheating)
A cause code that shows when the flow temperature climbs too quickly – in effect, an overheat lockout. Common triggers are an airlock, a sludge or limescale build-up, or a faulty thermostat (thermistor). It often shows up as the boiler overheating when you run hot water, because that is when heat demand peaks.
What to check: Check the pressure (1–1.5 bar cold), bleed your radiators, and make sure every radiator valve is open. Reset once. If the code comes straight back, the cause is usually inside the system – limescale, a pump fault or a sticking sensor – and needs an engineer.
One quick tell-tale for sludge: if a radiator is hot at the bottom but stays cold or tepid at the top, there is muck settled in the system. A power flush clears it and stops the boiler tripping on overheat again.
D5 / EA 229 – Frozen condensate pipe
EA 229 means the flame was lit and then lost during operation – a blocking fault, and in winter almost always a frozen condensate pipe (not to be confused with EA 227, where the boiler fails to light in the first place). D5 is the condensate-drainage fault behind the same problem. On floor-standing models with a condensate pump, such as the CDi Highflow, D5 points to the condensate pump itself rather than a frozen pipe.
What to check: Find the white 22mm pipe running from the boiler to an outside drain. Clear any ice with warm water, then insulate the pipe to stop it refreezing.
C6 215 – Fan speed problem
The fan is not running at the right speed, which affects combustion and flue gas removal..
What to check: Listen for unusual fan noise. Fan faults nearly always need an engineer – our boiler fan fault guide explains why.
Worcester fault codes by model
The section above covers the handful of codes people hit most and can often clear themselves. This is the full reference – every code, listed by model. Codes vary by range, so find your model below. Where a model comes as both combi and system versions, they share the same codes.
Greenstar i System & Combi
One of the UK’s most-installed boilers, with over a million units fitted. It comes as the 24i (24kW, smaller flats) and the 30i (30kW, average homes), plus system versions on the same codes. Now replaced by the Greenstar 4000, but still common in UK homes.
| Code | What It Means |
|---|---|
| A1 | Pump stuck or running dry |
| A7 | Domestic hot water sensor defect |
| A8 | Heat control module (HCM) invalid |
| C1 | Fan stopping during operation |
| C4 | Control box / HCM defective, or fan failed to stop |
| C6 | Fan speed too high or too low |
| C7 | Fan not running on start-up |
| CC | Outdoor sensor defect |
| D4 | Primary flow temperature rising too fast |
| E2 | Flow temperature sensor fault |
| E9 | Flue/high-limit thermostat tripped; water above 95°C |
| EA | No flame detected after ignition |
| FA | Flame detected after the gas valve closed |
| F0 | Gas valve or control box error |
| F7 | Ionisation detected before the burner started |
| FD | Power supply interrupted |
| 9U | Control box defective or loose |
Greenstar Si Compact
The same reliability as the Greenstar i in a smaller case – built for kitchen cupboards and tight spaces.
| Code | What It Means |
|---|---|
| 9A 362 | Incorrect HCM fitted |
| 9U 233 | HCM / code plug error |
| A1 281 | Pump stuck or air in the system |
| B7 257 | Internal / control board error |
| C1 264 | Airflow stopped during operation |
| C6 215 | Fan running too fast |
| C7 214 | Fan not running |
| D1 240 | Return sensor error / short circuit |
| D4 271 | Flow and safety sensor temperature difference too high |
| E2 222 | Flow sensor short circuit |
| E5 218 | Flow temperature too high |
| E9 219 / E9 224 | Safety sensor fault or flue gas thermostat overheating |
| EA 227 | No flame detected after ignition |
| F0 237 | Internal error |
| F7 228 | False flame detected |
| FA 306 / 36 | Gas valve leak or false flame fault |
| FD 231 | Power fault / interruption |
CDi Classic & Compact
The CDi Classic was a flagship combi and regular boiler before the Greenstar 8000 Style replaced it. The CDi Compact is the space-saving version for modern homes. These codes also cover older Greenstar CDi combis, including the 30CDi.
| Error Code | Meaning / Possible Fault |
|---|---|
| B1 | Code plug not detected |
| C6 | Fan speed too low or too high |
| E2 | Flow sensor fault |
| E9 | Safety temperature limiter triggered |
| EA | Flame not detected (possible gas supply issue) |
| FA | Flame detected after gas shut-off (gas valve fault) |
| FD | Reset button pressed accidentally |
CDi Highflow
A floor-standing combi built for large homes with heavy hot water demand.
| Error Code | Meaning / Possible Fault |
|---|---|
| A1 | Pump dry-run or air in the system |
| A5 / A7 | NTC sensor defect (tank or DHW) |
| C6 | Fan defect |
| D5 | Condensate pump failure |
| E9 | Safety temperature limiter tripped |
| EA | Flame not detected |
| FD | Reset button pressed accidentally |
Greenstar 8000 Style
Worcester’s modern flagship, from 30kW to 45kW, suited to larger homes with several bathrooms. It uses longer numeric codes.
| Error Code | Meaning / Possible Fault |
|---|---|
| 1017 W | Low water pressure |
| 1021 / 1022 B | Hot water sensor |
| 1073 / 1074 W | Flow temperature sensor short circuit / no signal |
| 227 V | No flame signal after ignition |
| 228 V | Flame signal without flame present (possible valve issue) |
| 229 B | Flame lost during operation (often a frozen condensate pipe in winter) |
| 2927 B | Flame failure during operation |
| 2964 B | Primary flow rate too low – insufficient flow through the heat exchanger |
| 2971 B | System pressure too low |
Note on 2964 B (also written 2964B): this means the primary (heating) flow rate through the heat exchanger is too low – the flow sensor on the supply pipe is not seeing enough circulation. Common causes are the flow sensor not seated properly or not making good contact with the supply pipe, the system not being full of water, or no circulation at all (a closed circuit, a stuck pump, or an airlock). Reset once. If it returns, an engineer needs to check the sensor seating and the circulation, and reset or recalibrate the flow settings where needed.
The trailing letter on 8000 Style codes is Worcester’s fault category, not part of the number: O is an operating message (not a fault), B is a blocking fault (clears itself once the cause is sorted), V is a locking fault (needs a manual reset), and W is a maintenance code. These line up with the five fault types above.
Worcester boiler symbols explained
Not everything on the display is a fault. Worcester uses symbols for normal modes too. Here is what they mean.
| Symbol | What It Means |
|---|---|
| Warning triangle | A fault needs attention. With a locking error it flashes next to the code. Do not ignore it. |
| Flashing code | A locking error. The boiler has shut down and needs the fault fixing, then a reset to clear it. |
| Spanner | Service due. The boiler still runs, but book a service soon. This is the service symbol people search for as the "spanner symbol". |
| Key / padlock | Child lock is on (newer Greenstar models). Hold the relevant buttons to turn it off. |
| Siphon fill mode | The boiler is filling its internal condensate trap. Normal on first fire-up or after a service. It usually clears itself within a few minutes. |
| Air purge (circular arrow) | The boiler is bleeding air automatically by pulsing the pump. Normal after a power-up or PCB change and usually lasts about 15 minutes. |
| Max / Min (flame) | The boiler is running at its maximum or minimum rate during a service check. Normal and should finish within 15 minutes. |
As a rule: if a symbol you do not recognise stays on screen for more than 15–30 minutes, treat it as a fault and look it up or call an engineer.
Basic troubleshooting you can try
Check the system pressure
Your gauge should read 1–1.5 bar when the system is cold. Low pressure is one of the most common causes of Worcester faults. To top up: find the filling loop (a braided hose with a valve at each end), open both valves slowly until the gauge reaches about 1.2 bar, close them, and check the pressure holds.
Thaw a frozen condensate pipe
In winter the white condensate pipe to an outside drain can freeze. Pour warm water slowly along its length – never boiling, as that can crack it. Then insulate it to stop it happening again. Our frozen condensate pipe guide covers the warning signs.
Reset the boiler
Many Worcester models reset with a button, or by holding the temperature dial at the reset position for about 3 seconds. Important: do not reset an EA code, as it can indicate a gas safety issue.
Check thermostat batteries
For a wireless thermostat showing an A21 code, replace the batteries and make sure the stat is within range of the boiler’s receiver.
When to call a Gas Safe engineer
Some faults always need a professional:
| Fault | Why It Needs an Engineer |
|---|---|
| EA / flame faults | No flame detected – a possible gas issue |
| F7 / false flame | Flame sensed when there should not be one |
| Gas valve errors (FA, F0) | Any fault involving gas components |
| Internal faults | PCB, pump or fan failures |
Never work on gas components yourself. Only Gas Safe registered engineers can legally and safely work on gas appliances. For a same-day fix, we handle Worcester boiler repair in London across the city.
Preventing Worcester boiler faults
Annual service
A regular boiler service catches problems before they cause a breakdown. It keeps the manufacturer warranty valid, improves efficiency, and extends the boiler’s life.
System cleaning and inhibitor
Every 2–3 years, a chemical clean and fresh inhibitor protects the system. Poor water quality causes most breakdowns – through limescale in the heat exchanger, corrosion, and sludge blocking pipes and valves.
Monthly checks
- Monitor the system pressure
- Listen for unusual noises
- Check for visible leaks
- Test the heating controls
- Inspect the external condensate pipe before winter
Print or bookmark this fault code list
Everything is on this one page. Bookmark it to find it fast, or use your browser’s print option to keep a copy – printing to PDF works the same way. There is no separate download; the model tables above are the complete list.
Worcester boiler repair in London
Found your code and it is not a quick fix? Our Gas Safe engineers diagnose and repair every Worcester model, carry genuine parts, and warranty the work.
Whether it is an emergency breakdown or a fault that keeps coming back, book Worcester boiler repair in London. For planned upkeep, see our annual boiler service in London.
