Worcester Bosch Fd 231 fault codewhat it means and how to fix it
Power to the boiler was cut while it sat in a lockout, so a fault happened before the interruption. On older Greenstars, Fd simply means the reset button was pressed by mistake.
Take care
What Fd 231 means
This is one of the codes whose meaning changed between Worcester generations, and the display you have tells you which meaning applies. On a Greenstar i or i System ErP, and on the CDi Compact, Si Compact and 27i/30i System Compact, the table reads "Fd 231 — electrical interruption fault — the power has been interrupted during a lockout". The boiler was already locked out on something else when the mains went off, and when power came back it flagged the interruption rather than the original fault.
Worcester's instruction to the engineer is to open the locking error history, where the real lockout will always be the code immediately before Fd, and then reset the appliance. On the Greenstar CDi Classic, on the earlier CDi combi, system and regular boilers, and on the Highflow, the same two characters mean something quite different: "Fd — reset button pressed by mistake — press reset button again".
There is no three-digit number on those displays. In both cases the fix begins with a reset, and in both cases the thing to be curious about is what came before. A Greenstar i showing Fd 231 after a power cut had a genuine lockout earlier — an ignition failure, an overheat — and that is the fault worth quoting to an engineer. A CDi Classic showing Fd was most likely reset by someone leaning on the panel, and if the code will not clear, Worcester's own fault-finding booklet moves straight to the control board.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Power cut or the boiler switched off during a lockout | A fused spur turned off, a tripped breaker or a supply interruption while the boiler was already locked out on another fault produces 231 when power returns. | Common |
| Reset button pressed when there was no fault | On the two-character displays of the CDi Classic era, Fd is Worcester's way of saying reset was pressed in error, and pressing it again clears it. | Common |
| Poor mains supply | A loose connection at the isolator or a supply that dips can look like repeated interruptions, and the boiler will keep logging them. | Occasional |
| Control board fault | If Fd will not clear after a proper reset with the power stable, Worcester's service booklet has the engineer change the control board. | Rare |
What to try yourself
Work out which display you have. Two characters with a three-digit number under them is the Greenstar i or Compact family; two characters on their own is the CDi Classic or an earlier Greenstar.
Greenstar i and Compact: press the reset button briefly once. Worcester's user guide says the word Reset and a tick appear briefly, and the boiler returns to normal if the reset succeeded.
CDi Classic: press and hold the reset button for three seconds. The reset button and the blue fault indicator stop flashing when it has taken.
If the boiler comes back with a different code, that is the fault that was there before the interruption. Look that code up rather than this one.
If it comes back with EA or another ignition code, do not keep resetting. Two attempts, then call a Gas Safe registered engineer.
Get a Gas Safe registered engineer to look at your Worcester Bosch Fd 231
We do not pass enquiries to a repair firm, so there is no form here. Find a Gas Safe registered engineer through the Gas Safe Register, and ask to see their registration card when they arrive — it is the register, not the van, that tells you they are qualified.
What it costs to fix
Typical repair cost
£0–£450
Time on site
10 minutes
Free to reset. If the control board has to be replaced, £250–£450 fitted, though that is the last resort in Worcester's own procedure.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
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Worcester Bosch Greenstar control board (PCB)
£250–£450Authorised Worcester parts distributor
Price checked 28 September 2026
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Related Worcester Bosch fault codes
- Blue light flashingGet it checkedOn a Greenstar with no display, the blue light is the fault code. Steady means healthy; a flashing pattern, read with the reset button, is a diagnosis Worcester publish in the installation instructions.Related: electronics and power
- F0Get it checkedThe boiler has found a fault inside its own electronics and stopped. F0 covers the control board and the burner control unit, and it needs an engineer.Related: electronics and power
- A7Get it checkedThe hot water temperature sensor has failed. Heating usually carries on as normal while the hot water runs cold, scalding, or swings between the two.Related: electronics and power
- Red light flashingGet it checkedOn a Worcester built before the Greenstar era, the flashing lights are the fault code. Slow means a lockout you can reset once; fast means a fault the boiler is waiting out or an engineer's.Related: electronics and power
- 9U 233Get it checkedThe heat control module is loose, missing or faulty. This small plug-in part carries the identity of your boiler, and nothing runs without it.Related: electronics and power
- 2980Stop — call an engineerSuper lock-out. Five locking faults were reset inside fifteen minutes while the boiler saw a potentially safety-critical condition, so it has locked itself against further resets. Only an engineer can clear it.Related: electronics and power
Own a Worcester Bosch boiler? Save it and its codes come first next time.
Related guides
Common questions about Worcester Bosch Fd 231
The power went off in a storm and now it says Fd 231. Is the boiler damaged?
Probably not. The code records that the interruption happened while the boiler was locked out, not that the interruption caused harm. Reset it. If it runs, note that it was locked out on something before the storm and keep an eye on it.
How does an engineer find the original fault?
The Greenstar i keeps the last eight locking errors in a history menu behind the engineer functions, and Worcester note that the real lockout is always the entry before Fd. That is why it is worth not resetting more than once — every reset adds another line to the history.
Why does my CDi Classic show Fd when I have not touched it?
Worcester's meaning for it on that range is a reset pressed by mistake, and a brush against the panel is enough. If nobody has been near it and it recurs, the button or the board behind it is worth an engineer's look.
Technical review
Not reviewed by an engineer
No engineer has read this page. Severity follows what the manufacturer publishes, and we would rather tell you that than let a byline imply a sign-off.
Sources and how we verified this
We establish the facts from the sources below and then write the explanation ourselves. We do not copy manufacturer wording and we do not host their manuals.
- Manufacturer technical and service documentation
This page has not been reviewed by an engineer, and we would rather tell you that than imply otherwise. The severity rating follows what the manufacturer publishes: where they say isolate the appliance and call someone, so do we.