Worcester Bosch FD Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch FD fault code mean?
The FD code appears on your Worcester Bosch boiler's display to indicate that the unit has detected an interruption to its mains power supply, or that the reset button has been activated — either deliberately or by accident. It is essentially the boiler's way of flagging that something disrupted its normal power state. On models that show a numeric sub-code alongside FD, the most common is FD 231, which specifically points to a detected mains power interruption. In most cases FD is not a sign of a serious internal fault, but if it keeps returning after a reset it warrants closer investigation.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Mains power interruption (FD 231) Common
A brief or sustained loss of electrical supply to the boiler — caused by a household power cut, a tripped MCB or RCD in the consumer unit, or a loose connection at the boiler's fused spur — is the most frequent trigger for FD. When power is restored, the boiler flags the event with this code rather than restarting silently.
- Accidental reset button press Common
The reset button on Worcester Bosch boilers is relatively accessible and can be nudged unintentionally during cleaning, decorating, or general activity near the boiler. A stray press triggers the FD code even when nothing is actually wrong with the appliance.
- Faulty or intermittent electrical supply to the boiler Sometimes
Loose wiring at the fused spur, a worn plug connection, or an ageing dedicated circuit can cause repeated micro-interruptions that the boiler registers as power loss events. This would cause FD to return shortly after each reset.
- PCB fault Rare
If no external power issue can be found and the FD code keeps reappearing, the printed circuit board itself may be misreading voltage levels or logging spurious reset events. This is the least common cause but becomes more likely on older boilers or after a significant electrical event such as a power surge.
How to fix it
- Check the household power supply DIY safe
Before touching the boiler, check whether other appliances in your home are working normally. Go to your consumer unit (fuse box) and look for any tripped MCBs or RCDs. If you find one, switch it back on. Also verify that the boiler's fused spur switch (usually mounted on the wall near the boiler) is turned on and that no fuse has blown.
- Reset the boiler DIY safe
Once you are satisfied the power supply is normal, press and hold the reset button on the boiler fascia for approximately three seconds, then release it. The boiler will go through its startup sequence. Allow a minute or two for it to complete. If the FD code clears and the boiler fires up successfully, monitor it over the next day or so to confirm it stays clear.
- Make a note of any follow-on fault codes DIY safe
If, after resetting, a different fault code appears on the display, write it down before pressing anything else. A secondary code can give an engineer valuable diagnostic information. Search for that code separately on BOYLA to understand what it means.
- Repeat the reset no more than twice more if the code returns quickly DIY safe
If FD comes back within minutes of the first reset, try resetting once or twice more (no more than two to three attempts in total). If the boiler continues to show FD or fails to stay running, stop resetting — repeated attempts will not fix an underlying electrical fault and may mask other issues.
- Call a Gas Safe registered engineer if the fault persists Gas Safe engineer
A returning FD code that cannot be cleared by resetting, or one that clears only to come back within hours, points to an underlying electrical or PCB issue that must be diagnosed and repaired by a Gas Safe registered engineer. They will check the internal wiring, the fused spur circuit, and the PCB for faults. Do not open the boiler casing yourself, as this is dangerous and will likely invalidate any remaining warranty.
Parts you may need
- Printed circuit board (PCB) · from £220
- Fused spur switch (boiler isolation switch) · from £15
- Boiler mains cable and plug assembly · from £25
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £80–£300, depending on the underlying cause.
Frequently asked questions
What does FD 231 mean on a Worcester Bosch boiler?
FD 231 is the specific sub-code that appears on certain Worcester Bosch models (particularly the CDi Compact and Greenstar ranges) to confirm the FD event was triggered by a detected mains power interruption. If you see FD 231, start by checking your consumer unit for a tripped breaker and the boiler's fused spur, then attempt a reset. If FD 231 keeps returning with no obvious power supply issue, ask an engineer to inspect the wiring and PCB.
Can I fix the FD fault code myself?
In many cases, yes. If the code appeared after a power cut, a tripped breaker, or an accidental button press, a straightforward reset will clear it and the boiler will run normally. Checking your consumer unit and fused spur is also well within DIY territory. However, if the code keeps coming back, the cause is likely an internal electrical fault or PCB problem — work of that nature must be carried out by a Gas Safe registered engineer.
How much does it cost to fix a persistent FD code in the UK?
If a reset and a check of the fused spur clears the fault, there is no cost at all. If you need an engineer, a diagnostic visit typically costs £80–£150 including callout. Minor electrical repairs such as replacing a fused spur or a damaged supply cable usually come to £100–£200 all-in. A PCB replacement — the worst-case scenario — can cost significantly more, often £350–£600 including parts and labour, and tends to sit at the higher end in London and the South East. If your boiler is over ten years old and a PCB replacement is recommended, it is worth getting a new boiler quote at the same time for comparison.
Will the FD code clear itself, or do I always need to reset?
The FD code will not clear on its own — Worcester Bosch boilers require a manual reset after logging a power interruption. This is a deliberate safety feature so that the boiler does not silently restart without you knowing a disruption occurred. A single press-and-hold of the reset button for three seconds is normally all it takes, provided the underlying power supply is stable.