This fault can involve incomplete combustion and carbon monoxide.
If anyone in the property feels sick, dizzy or drowsy, or you can smell gas: open the windows, leave the building, and do not switch anything on or off. Then call the National Gas Emergency Service.
0800 111 999Worcester Bosch C1 264 fault codewhat it means and how to fix it
Airflow stopped part way through a firing cycle. The fan has quit or the flue is obstructed, and combustion gases may not be leaving safely.
Take care
Get a Gas Safe registered engineer to look at your Worcester Bosch C1 264
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 happened around the time it stopped?
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 carbon monoxide alarm went off
Do not treat this as a boiler repair question. Products of combustion have reached the room, and people come first.
Everyone outside into fresh air, ring 0800 111 999, and get medical advice for anyone feeling unwell.
It runs for a few minutes then locks out every time
A repeatable failure once warm fits a fan giving up under heat or a restriction that only matters at full flow.
Leave it off and describe the timing to the engineer. It genuinely narrows the diagnosis.
There are birds or nesting around the flue outside
A partially blocked terminal is a common cause and one an engineer can confirm quickly from outside.
Do not poke anything into the flue. Mention what you have seen and let it be inspected properly.
What C1 264 means
Worcester publish this one exactly as it appears here. Their Greenstar i fault table gives C1 264 under the heading "fan/airflow fault" with the description "fan stopped during operation", and the checks they list are the fan harness and connector, 230 V ac across the brown and blue wires, and the operation of the fan itself, replacing it if necessary.
Note what is not on that list: Worcester do not attribute this code to a blocked flue, and an earlier version of this page did. The distinction that matters is the timing rather than the flue. C1 264 is reported when the boiler loses airflow during operation rather than at start-up. The fan draws air in for combustion and pushes the products out through the flue, and the boiler watches that this continues for as long as the burner is lit.
Losing it mid-cycle is treated more seriously than never establishing it, because the burner has already been running and there is a real prospect that exhaust gases were not being carried away for some part of that time. The usual causes are a fan failing under load, a loss of power or signal to it, or a flue that has become restricted. Whatever the cause, the possibility that combustion products entered the room is what drives the response: leave it off, and get it checked before it runs again.
What causes it
| Cause | What is actually happening | How likely |
|---|---|---|
| Fan failing once warm | Worn bearings often turn freely from cold and then stall as the casing heats and clearances close up. | Common |
| Flue obstruction | Nesting material, debris or a collapsed liner narrows the path until the fan can no longer maintain flow. | Common |
| Loss of power or control signal to the fan | A connector that expands slightly with heat can break contact only once the appliance is up to temperature. | Occasional |
| Condensate backing up into the flue path | A blocked trap or siphon can fill enough of the passage to disturb the airflow the boiler is monitoring. | Occasional |
Can you fix it yourself?
Stop — this needs an engineer
What it costs to fix
Typical repair cost
£120–£400
Fan assembly £220–£400 fitted. Flue clearance and test £120–£280, more where access is difficult. A combustion check should follow either.
Typical UK prices including parts and labour, updated September 2026. Your quote may differ.
Parts you may need
We may earn a commission if you buy a part through one of these links. It does not change what you pay, and it does not affect which parts we list.
Worcester Bosch Greenstar fan assembly
87161431070£130–£250Authorised Worcester parts distributor
Price checked 28 September 2026
Condensate trap and siphon
COND-TRAP£15–£38Plumbing merchant
Price checked 28 September 2026
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Related Worcester Bosch fault codes
- C6 224Get it checkedThe fan is not reaching the speed the boiler asked for, so combustion cannot be confirmed as safe and the burner has been prevented from firing.Related: fan and flue
- C7Get it checkedThe fan is not running at all, as distinct from running at the wrong speed. The burner is locked out until it is fixed.Related: fan and flue
- D5Get it checkedThe condensate pump has failed or cannot discharge. Acidic water will back up inside the appliance, so it needs attention promptly.Related: fan and flue
- 2910Stop — call an engineerFault in flue system. The boiler has detected a problem with its flue and locked out. Worcester's checks are obstructions, the flue integrity test and water in the sump. Not a code to reset repeatedly.Related: fan and flue
- C4 273Usually simple to fixThe fan has run continuously for 24 hours, so the boiler has paused firing for two minutes as a precaution. Something has been calling for heat non-stop, and that is what to find.Related: fan and flue
- EA 227Stop — call an engineerThe boiler tried to light and never detected a flame, so it has shut the gas off and locked out. This is the most common Worcester fault code.Related: same brand
Own a Worcester Bosch boiler? Save it and its codes come first next time.
Related guides
Common questions about Worcester Bosch C1 264
Is this worse than a fan fault at start-up?
Yes, and for a specific reason. If the fan never starts, the boiler refuses to light and nothing has burned. C1 264 means the burner was already alight when airflow was lost, so there is a window during which exhaust may not have been leaving properly.
Do I have a carbon monoxide problem?
Not necessarily, and the code alone cannot tell you. The boiler stopped precisely to prevent one. But because the burner was running when airflow failed, it must be treated as a possibility until an engineer has tested the flue and combustion. If you do not have a CO alarm, fit one.
How is it different from C6 and C7?
They describe the fan at other moments — running at the wrong speed, or not starting at all. C1 264 is specifically airflow ceasing during operation. Same components, different point in the cycle, and a different level of concern.
What does the repair usually come to?
A fan is £220 to £400 fitted. Clearing and testing a flue is £120 to £280, more if scaffolding or roof access is needed. Both should end with a combustion analysis to confirm the appliance is burning correctly.
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
- Trade body guidance
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.