Worcester Bosch F0 fault codewhat it means and how to fix it
The 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.
Take care
Get a Gas Safe registered engineer to look at your Worcester Bosch F0
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.
Has anything happened to the boiler recently?
The right answer depends on what you can see. Pick the one that matches.
Choose the option on the left that matches what your appliance is doing, and the answer for that case appears here.
A part was fitted in the last few weeks
Suspect the work rather than the boiler. A board fitted without the correct identification module, or a plug left half-home, produces F0 immediately.
Go back to whoever carried out the work before paying anyone else to diagnose it.
It clears on reset and comes back days later
Intermittent behaviour points at a connection rather than a dead component. A part swap based on a guess here is how people end up paying twice.
Ask the engineer to check and reseat the internal connectors before ordering anything.
There has been a leak or water damage near the boiler
Moisture on electronics causes exactly this. It can also make a board fail permanently some weeks after it dried out.
Mention the leak — it changes what the engineer looks at first and it may be an insurance matter.
What F0 means
F0 is Worcester reporting a fault in its own control electronics rather than in the gas, water or flue. What makes F0 unusual is how wide the range behind it is: everything from F0 237 to F0 290 shows on the display as F0. Some of those suffixes point at the burner control unit, which Worcester documentation also calls the KIM or boiler identification module.
Others point at the control box itself, or at cabling with a pinched or broken conductor. F0 278 is different again — it means a self-test of the sensors failed, not that any one part is dead. This is precisely why the three digits are not optional. Two boilers both displaying F0 can need entirely different parts, and quoting only the letters leaves the engineer guessing on your time.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Burner control unit or KIM failure | The module that holds the boiler identity and drives the burner sequence has failed or lost contact with the board. | Common |
| Loose or poorly seated plug | Connectors behind the fascia work loose over years of heating and cooling, and one pin lifting is enough. | Common |
| Damaged cabling inside the case | A harness pinched when a panel was refitted eventually breaks a conductor and produces intermittent internal errors. | Occasional |
| Control box failure | Concluded last, after the connections and the burner control unit have both been checked and cleared. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£150–£600
Reseating a connector may be a call-out only, £80–£150. Burner control unit £220–£380. Control board £350–£550 fitted.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Own this appliance and had this code? . Nothing is published until a person has read it.
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
- 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
- Fd 231Get it checkedPower 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.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 F0
My display only shows F0 with no numbers. What now?
Some models alternate slowly and the second half is easy to miss, so watch the display through a full cycle. If it genuinely never shows a suffix, an engineer can read the fault history through the service connection.
Is a new control board worth it on an older boiler?
It depends on what else is worn. On a boiler past fifteen years with a tired heat exchanger and a failing diverter valve, a board approaching £500 fitted is money towards a replacement appliance instead. On a twelve-year-old unit that has otherwise been reliable, it is usually the right call.
Can I reset it?
Once is reasonable, in case the fault was a momentary glitch. Repeated resetting achieves nothing on an internal electronics fault, because nothing about the condition changes between attempts.
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
- Manufacturer support portal
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.