Worcester Bosch C1 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch C1 fault code mean?
The C1 fault code on Worcester Bosch boilers — most commonly displayed as C1 264 on Greenstar i, Si, CDi, and Greenstar 1000/2000 models — indicates that the boiler's fan has stopped operating or has lost speed during a heating or hot water cycle. The fan is responsible for drawing fresh air into the combustion chamber and expelling flue gases safely outside. When the air pressure switch detects that airflow has dropped or disappeared, it signals the PCB, which shuts the boiler down as a safety measure. Without a working fan, dangerous combustion gases could build up inside the appliance. Note: on some older Worcester models such as the R25 HE, C1 can indicate an ignition fault rather than a fan issue — always cross-reference with your boiler's model documentation if you are unsure.
General guidance only — not a substitute for professional advice. 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
- Faulty or worn fan motor Common
The fan motor itself is the most frequent culprit. Over time, the motor windings can degrade or the bearings wear out, causing the fan to spin too slowly or stop altogether. You may hear an unusual grinding or whirring noise before the fault appears, which is a useful early warning sign.
- Blocked airway or flue restriction Common
Debris, nesting material, or a build-up of dirt can partially or fully obstruct the air intake or flue outlet, reducing airflow to the point where the pressure switch triggers a lockout. The fan motor itself may still be functional in this scenario.
- Wiring or connector fault Sometimes
Loose, corroded, or damaged wiring between the fan, air pressure switch, and PCB can cause intermittent or complete loss of the fan signal. This is a relatively straightforward repair for an engineer but cannot safely be investigated by a homeowner.
- Faulty air pressure switch Sometimes
The air pressure switch monitors the draft created by the fan via a thin rubber hose. If the switch itself has failed, or the hose has split or become blocked, the boiler may shut down even when the fan is spinning perfectly normally. An engineer can test the switch with a multimeter to confirm.
- PCB fault Rare
In rare cases the PCB fails to send the correct voltage to the fan, or misinterprets the fan feedback signal. This is usually only suspected once the fan, wiring, and pressure switch have been ruled out.
How to fix it
- Check your gas supply is working DIY safe
Before assuming the boiler is at fault, confirm that other gas appliances in your home (hob, gas fire) are working normally. If there is no gas supply, contact your gas supplier rather than attempting a boiler reset.
- Listen for unusual fan noises before resetting DIY safe
If it is safe to do so, briefly power the boiler on and listen near the casing for any grinding, rattling, or complete silence from the fan area. This information is useful to pass on to your engineer and may help confirm a worn motor.
- Inspect the visible flue terminal outside for obstructions DIY safe
Go outside and check the flue outlet (usually on an external wall or roof) for obvious blockages such as leaves, bird nesting material, or ice in freezing weather. Do not insert anything into the flue — simply remove loose external debris if it is safe to reach.
- Reset the boiler (maximum 2–3 times) DIY safe
Press and hold the reset button for around 3 seconds. If the boiler fires up but the C1 code returns shortly after, do not keep resetting — repeated lockouts indicate an underlying fault that needs professional diagnosis and could mask a worsening problem.
- Call a Gas Safe registered engineer to inspect the fan and pressure switch Gas Safe engineer
An engineer will remove the casing, check the fan motor speed and electrical supply, inspect the air pressure switch and its connecting hose, and test wiring continuity. They will confirm whether the fan needs cleaning, repairing, or replacing, and will also check the PCB output voltage if the fan appears physically sound.
- Allow the engineer to replace the faulty component Gas Safe engineer
If the fan motor is confirmed as failed, the engineer will source a compatible replacement — Worcester Bosch Greenstar fan assemblies are widely stocked. If the pressure switch or wiring is the cause, these are generally quicker and cheaper to fix than a full fan replacement.
Parts you may need
- Fan assembly (Worcester Greenstar compatible) · from £155
- Air pressure switch · from £35
- Pressure switch connecting hose · from £12
- Fan wiring harness/connector · 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 £250–£420, depending on the underlying cause.
Frequently asked questions
Is the C1 264 code dangerous — can I keep using my boiler?
You should not attempt to run the boiler while it is displaying C1 264. The lockout exists because the fan is not operating correctly, meaning flue gases cannot be expelled safely. Repeated forced resets without resolving the underlying fault could create a risk and will not fix the problem. Get it inspected promptly, especially if you have no heating or hot water in cold weather.
How much does it cost to fix a Worcester Bosch C1 264 fan fault in the UK?
For most homeowners the total bill — parts and labour — falls between £250 and £420. The fan assembly itself typically costs around £150–£180 from a plumbers' merchant, and labour for the replacement usually adds £100–£200 depending on the engineer's rates and your location. If the cause turns out to be a blocked airway, split pressure-switch hose, or loose wiring rather than a failed motor, the repair can be considerably cheaper. In rare cases where the PCB is at fault, costs can rise significantly — a PCB replacement can run to £400–£600 or more — but this is not the typical outcome for a C1 264 code.
My boiler is showing C1, not C1 264 — is it the same fault?
Not necessarily. On modern Greenstar i, Si, and CDi series boilers, C1 264 is the standard fan-interruption code and the display will usually show the sub-code 264 alongside C1. On older Worcester models such as the R25 HE, C1 on its own can indicate an ignition failure rather than a fan fault. Check your boiler's model number and user manual, or describe the exact display reading to your engineer so they can diagnose the correct fault.
Can a C1 264 fault be prevented with regular servicing?
Yes — annual servicing by a Gas Safe engineer is one of the most effective ways to catch fan issues early. During a service, the engineer will check fan speed, inspect for debris build-up around the air intake and flue, and test the pressure switch, meaning a developing problem can often be caught before it causes a full lockout. Keeping the area around your boiler clear of dust and ensuring external flue terminals remain unobstructed also helps.