Worcester Bosch Boiler C6 Error Code

Fan running too slowly on Worcester Bosch boilers.

Worcester Bosch All Worcester Bosch boiler codes

May need a pro

The combustion fan isn't reaching the speed the control board expects, so the boiler won't fire. Worcester's booklet points at a loose fan connector, low mains voltage, a damaged fan cable, the fan itself or the PCB.

Compatible models

In the user instructions for Greenstar CDi Classic ErP combis and HighFlow 440CDi and 550CDi ErP boilers, and the engineer's booklet for CDi Classic combi, system and regular models.

Also shown as

No other codes are listed for this fault.

Difficulty

Try the basic checks, but the usual fix is a technician's job.

How to fix
When to call a pro
Parts
FAQ

Not sure you are reading the code right? See how to read Worcester Bosch boiler codes.

Safety first: never take the casing off a gas boiler. If you smell gas, open windows, don't use light switches, turn the gas off at the meter if you can and call your gas emergency number from outside. A carbon monoxide alarm going off means the same: switch the boiler off, get fresh air and call.

How to fix Worcester Bosch C6

Restart the boiler once
Turn it off at the fused spur for a minute and back on. If other things in the house are flickering or tripping, mention it to the engineer, since low supply voltage is one of the causes.
Leave it off if C6 returns
Note the code and book a visit. The fan sits behind the sealed front casing.

When to call a technician

A Gas Safe engineer needs to test the fan, its plug and lead and the board.

Parts linked to C6

These are the parts an engineer usually checks for this code. They sit inside the sealed casing, so leave them to a Gas Safe registered engineer.

Frequently asked questions

Which Worcester Bosch models show the C6 code?

In the user instructions for Greenstar CDi Classic ErP combis and HighFlow 440CDi and 550CDi ErP boilers, and the engineer's booklet for CDi Classic combi, system and regular models.

Can I fix Worcester Bosch C6 myself?

Only the outside checks above. If they don't clear C6, the fix is inside the boiler and needs a Gas Safe registered engineer.

Other Worcester Bosch boiler codes

Last reviewed 2026-10-21. Codes and steps can vary by model; check your owner's manual.

Sources we checked