C6 215 on a Worcester Bosch boiler means: fan running too fast. The fan pushes waste gases out through the flue. The boiler has detected that it isn't running at the right speed, so it won't light.
This code applies to Worcester Bosch Greenstar Si Compact, Greenstar i and CDi Compact. Codes can mean different things on different models, so check the display against your boiler's user manual.
What you can safely check
- From the ground, check that the flue terminal outside isn't blocked by a bird's nest, leaves or plants. Don't climb a ladder to clear it.
- Press reset once, following the instructions in your user manual.
When to call an engineer
Fan faults need a Gas Safe engineer — the fan, its wiring or the control board may need replacing.
Never remove the boiler casing yourself — everything behind it must be handled by a Gas Safe registered engineer. If you smell gas, open windows, turn the gas off at the meter, and call the National Gas Emergency number on 0800 111 999.
Repair it, or replace it?
If your boiler is over 10 years old, compare a repair against a new combi before you pay for parts.
Applies to: Worcester Bosch Greenstar Si Compact, Greenstar i and CDi Compact
Meaning checked against: HomeServe — Worcester Bosch boiler faults
Last reviewed November 2026. Always follow your boiler's own user manual.