Boiler fault codes
Worcester C6 Fault Code: Fan Running at the Wrong Speed
Published
Worcester Bosch display
C6
What it means
The boiler measured its fan running at the wrong speed and locked out, because it cannot burn gas safely without the right amount of air. On Greenstar models, 215 after C6 means too fast and 216 means too slow.
Safe to check yourself
- Look at the flue terminal outside for anything blocking it, such as a bag, a nest or drifted snow, without climbing a ladder
- Note whether lights have been flickering or the power has dipped
- Press and hold reset for about five seconds, once
Call an engineer if
- You smell gas: open windows, turn off at the meter if safe, do not touch switches, then leave and call 0800 111 999
- C6 comes back after one reset
- The boiler makes a grinding, rattling or roaring noise before locking out
- You smell burning or see scorching around the casing: switch off at the fused spur
C6 on a Worcester Bosch boiler is a fan fault: the fan speed the boiler measured did not match the speed it asked for, so it locked out. On Greenstar models, 215 means too fast and 216 means too slow. Reset once. If C6 returns, the fan, its wiring or the supply voltage needs testing.
What does C6 mean on a Worcester boiler?
Worcester groups fan faults under two letters. Its manuals for Greenstar i and CDi Compact models list:
- C6 215: fan speed too high
- C6 216: fan speed too low
- C7 214: fan does not run during start-up
- C7 217: fan stopped during operation, or no airflow after a set time
Sources disagree on the edges. An older Greenstar CDi service booklet lists C6 simply as "fan speed too low" with no cause code, and some third-party guides lump every fan and flue problem under C6. Go by the cause code on your display and your own boiler manual.
Why is my Worcester fan running at the wrong speed?
The fan has a speed signal that the control board reads constantly. Worcester's fault-finding order for C6 goes from cheapest to dearest: is the fan plug properly connected, is the mains supply within tolerance (230 V, plus or minus 10%), does the fan cable have continuity, is the fan itself defective, and only then the control board.
That second check matters more than people expect. On a weak supply the fan cannot reach speed, and Worcester tells engineers to see whether the fault clears with some heavy electrical appliances switched off. The most common result on a boiler more than a few years old, though, is a worn fan: bearings dry out, it slows, gets noisy, and eventually fails the speed check.
A fan that sounds like a jet engine or rattles before the fault appears is a strong hint. The boiler noise like an aeroplane guide covers that symptom on its own.
What can I check before calling an engineer?
Not much, and that is honest: the fan, its wiring and the board are all inside the sealed casing, which you should never open. From outside, look at the flue terminal for anything obviously blocking it. Think about whether the lights have been dimming or the power has tripped; if so, mention it, because it changes where the engineer starts.
Then press and hold reset for about five seconds. If the boiler fires and runs normally for the rest of the day, note the time and keep an eye on it. If C6 comes back, leave it locked out and book a Worcester boiler repair.
What does a C6 repair involve?
The engineer tests the fan connector and cable, measures the supply, and checks the fan. Replacing a fan means removing the air/gas assembly, so the burner seal and combustion readings have to be checked afterwards, which is gas work. Gas work is carried out by Gas Safe registered engineers.
Parts vary by model. A fan costs a good deal more than the plug and cable checks that come before it, and a control board costs more again, which is why the cheap checks come first. Our side is simple: the £60 call-out, then the repair price agreed on site before work starts. Our page on the cost of a boiler call-out explains it. For other lockouts, see Worcester EA 227.
Questions people ask
Can I keep resetting a C6 fault?
One reset is reasonable. If C6 keeps returning, the fan is failing the boiler's own safety check, and repeated restarts will not fix it.
Is C6 the same as C7 on a Worcester?
Both are fan faults. C6 means the fan runs at the wrong speed; C7 means it did not run or stopped. The Worcester fault code index covers the others.