C6 on a Worcester Bosch is a fan fault: the fan that pulls air through the boiler and pushes exhaust gases out isn’t running at the speed the boiler expects, so it locks out. We’re Clever Energy Boilers, Gas Safe registered and accredited Worcester Bosch installers based in Bingley, serving Yorkshire and the Humber, the North West and the Midlands. If your Worcester is an older boiler that keeps showing error codes, a replacement Worcester Bosch boiler is the better option longer term for efficiency and to save on repair bills.
Because the fan is part of the combustion system, C6 is a code to handle with care. You can do a couple of simple things, but most of the work belongs with a Gas Safe registered engineer. Here’s the detail.
What does the C6 error code mean on a Worcester Bosch boiler?
The fan has to reach the right speed before the boiler will light, and C6 says it didn’t. Which direction the fault goes depends on the model, and sources don’t fully agree. Si and CDi Compact boilers describe the fan as running too fast, shown as C6 215. The CDi Classic Combi describes it as too slow. The Greenstar i and CDi Classic Regular mention either too fast or too slow. The CDi Highflow simply reports a fan defect.
The sensible reading: the fan isn’t where it should be. Check the cause code on your display, as it tells you more than the letter alone.
What causes a Worcester C6 fault?
- A fan that is wearing out or has failed
- A damaged fan lead or loose connector
- A blocked or restricted flue, so air can’t move as expected
- A fault with the sensing that proves airflow
- A circuit board fault, which our guide on boiler PCB faults covers
Is a Worcester Bosch C6 fault dangerous?
The lockout is the safety system working, since a boiler shouldn’t fire without proven airflow. But fans and flues affect how safely a boiler burns gas, so please take it seriously. Make sure your carbon monoxide alarm is working. Signs of carbon monoxide include headaches, dizziness and nausea, particularly when the boiler is on. If you suspect it, open windows, leave the house and call the National Gas Emergency Service on 0800 111 999.
What can I check safely when a Worcester shows a C6 error?
Honestly, not a lot, and that’s as it should be. Two things are reasonable:
- Go outside and look at the flue terminal, the pipe where the exhaust leaves the house. If you can see something obviously blocking it from the ground, such as a nest, leaves or debris, note it. Don’t climb up to clear it.
- Switch the boiler off, wait a minute, and press reset once.
If C6 returns, stop. Don’t remove the casing, don’t touch the fan or its wiring, and don’t keep resetting. A Gas Safe registered engineer needs to check the fan, lead and connector.
Why does the Worcester C6 fault code come and go?
An intermittent fan fault often means worn bearings or a loose connection. The fan works some days and not others, and that makes the code seem random. Over time the good days get fewer.
Should I repair or replace a Worcester Bosch with a C6 error?
A new fan on a young boiler can be a reasonable repair. On an older one, consider replacing the boiler when:
- It’s over 8 years old
- This is the second fault code you’ve had this year
- The fan is noisy as well as faulting
- You want to stop depending on a boiler you can’t trust
A modern Worcester Bosch is quieter, more efficient and comes with the fan, controls and sensors all up to date.
Arranging a new Worcester Bosch
We cover Yorkshire and the Humber, including Bingley, Keighley, Halifax and Wakefield, the North West including Manchester, Stockport and Crewe, and the Midlands, including Leicester, Stoke-on-Trent and Telford. See our Worcester Bosch boiler installation page or get your online quote. For a chat about a new boiler, call 0330 055 2210 between 8am and 8pm on weekdays.
Worcester Bosch C6 fault code FAQs
Is the Worcester C6 error a fan that is too fast or too slow?
It depends on the model. Compact models describe too fast, the CDi Classic Combi too slow, and others either. Your cause code helps narrow it down.
Can I fix a Worcester C6 fault myself?
Only to the extent of checking the flue terminal from the ground and resetting once. Fan and wiring work is for a Gas Safe registered engineer.
Does a C6 error code on a Worcester mean carbon monoxide is leaking?
Not necessarily, but fan and flue faults affect combustion, so check your CO alarm and act on any symptoms.
Why is my Worcester noisy before showing a C6 fault?
A failing fan often whines or rattles before it gives up. Treat unusual noise as an early warning.
Is it worth replacing an old Worcester Bosch with a fan fault code?
If the boiler is over 8 years old, replacing it usually works out better than repairing it.
More Worcester Bosch error codes
C6 sits with the sensor and fan-related codes. Before this one, have a look at the Worcester Bosch E9 fault code; after it, the Worcester Bosch D1 fault code covers the next code in the set. The full list sits on our Worcester boiler error codes guide.
