What it means
What C6 is telling you
C6 means the boiler's control board asked the fan for a certain speed and didn't get it. The fan clears combustion gases through the flue, so the boiler will not light without it.
Bearings wearing out is the most common reason — often preceded by weeks of a rattling or grinding noise from the boiler that people learn to ignore.
It can also be a wiring fault to the fan, a blocked flue, or occasionally the PCB itself misreading the signal.
Before you call
Safe checks you can do yourself
- Think back — has the boiler been noisier than usual recently? That points firmly at the fan
- Check the flue terminal outside isn't blocked by leaves, a nest or snow
- Reset once; a fan fault usually returns quickly
Never remove the boiler casing or work on the sealed combustion chamber yourself — by law that’s Gas Safe registered engineers only. If you smell gas, call 0800 111 999 immediately.
How we fix it
What we do on the visit
- Fan tested for speed and current draw before any part is ordered
- Fan replaced with the correct Worcester part, not a generic
- Flue inspected end to end for blockage or damage
- Wiring loom and PCB output checked so we're not replacing a good fan
How urgent is it?
The boiler is locked out and unusable. Book a repair — do not attempt to run it.
Costs
What a repair costs
Our diagnostic visit is £99 inc VAT and it comes off the bill if we carry out the repair. We give you a fixed price before touching anything — no hourly rates, no surprises on the invoice.
We’re Gas Safe registered, Which? Trusted Trader endorsed and rated 4.9 across 206+ reviews. We carry the common Worcester Bosch and Viessmann spares on the van, so most faults are fixed on the first visit rather than booked back in.
Common questions
How much is a boiler fan replacement?
Usually £250–£420 inc VAT fitted depending on the model. We confirm the fixed price before we start.
Can I use the boiler with a C6 fault?
No, and it won't let you. The fan clears combustion products through the flue, so the boiler correctly refuses to fire without it.
Is a fan fault worth fixing?
On a boiler under ten years old, yes. On an older unit where the fan is £400 fitted, we'll show you that figure against a new boiler and let you decide with the numbers in front of you.
Book it in
Get an engineer out
Step 1 / 5
60 second boiler quote
No callbacks unless you want one
What can we help with?
Pick the option that fits — we'll tailor the next questions.
More help