Quick answer: The C7 fault code (often shown as C7 214 or C7 217) means your Worcester Bosch boiler’s fan isn’t running when it should be, either failing to start or stopping during operation. Without the fan there’s no safe airflow through the combustion chamber, so the boiler locks out immediately. This is a combustion safety fault and needs a Gas Safe registered engineer in nearly every case.
Written by the engineering team at Edinburgh Boiler Company, Scotland’s number one boiler installer. C7 is a fault where the diagnosis is usually quick and the answer is usually a new fan, and knowing that up front saves customers a lot of uncertainty.
What does C7 mean on a Worcester boiler?
C7 means no fan movement detected. When the boiler receives a demand for heat, the very first thing it does is run a pre-purge, spinning the fan to clear the combustion chamber and flue of any residual gases before the burner lights. If the control board doesn’t see the fan’s feedback signal confirming it’s turning, the sequence stops there. The burner never gets a chance to fire.
That’s the boiler doing precisely what it should. A burner firing with no fan running would produce combustion gases with nowhere to go, and that’s the scenario every airflow interlock exists to prevent.
Is C7 the same as C6?
No. They’re both fan faults, but they describe opposite situations, and which one you have narrows the likely cause considerably.
| Code | What the boiler sees | Most likely cause | Typical outcome |
|---|---|---|---|
| C6 215 / C6 216 | Fan turning, but at the wrong speed | Worn bearings, flue restriction, debris | Sometimes a clean or flue clear |
| C7 214 / C7 217 | Fan not turning at all | Failed motor, no power to fan, wiring fault | Usually a fan replacement |
C6 leaves room for a cheap fix, because a restriction can be cleared. C7 usually doesn’t. Something has stopped the fan turning entirely, and that’s a hardware problem rather than an airflow problem.
What causes a C7 fault?
| Cause | How common | What’s happening |
|---|---|---|
| Failed fan motor | Very common | Bearings seized, or the motor windings have gone |
| Faulty wiring or connector to the fan | Common | Corroded plug, damaged loom, or a connector vibrated loose |
| PCB not powering the fan | Occasional | The board’s output stage has failed, so the fan gets no signal |
| Airflow restriction stalling the fan | Occasional | Severe blockage in flue or venturi preventing rotation |
| Air pressure switch fault | Occasional | On older models, presents alongside fan symptoms |
| Fan seized after a period of inactivity | Common in autumn | Bearings dry out over summer and the motor can’t break free |
That last one is worth dwelling on. A fan that has been running with tired bearings all through the previous winter will often keep going right through summer at low demand, then fail the first time it’s asked for a proper cold-morning start. This is why we get a run of C7 calls every September and October across Edinburgh and the Lothians, right as people switch the heating back on.
Why is timing so predictable with C7 faults in Scotland?
Because Scottish heating patterns concentrate the stress. A boiler here runs far more hours per year than one in the south of England, so fan bearings accumulate wear faster. Then there’s a relative lull over summer, when most Scottish households still use the boiler for hot water but nothing like the winter workload.
Bearings that are marginal do fine at low, occasional demand. What kills them is the transition back to full duty in autumn, when the fan is asked to start from cold and run hard, several times a day, for the first time in months. A marginal bearing doesn’t survive that, and you get C7 on a cold Tuesday morning in October.
There’s also a damp factor. Boilers in unheated garages, outhouses and cold utility spaces, which is a common arrangement in Scottish rural and semi-rural properties, sit in higher humidity for months. Moisture gets into the fan housing and connectors, and corrosion does the rest.
What can I safely do myself?
Three things, none of which involve the casing.
1. Reset the boiler once. Hold the reset button for three to five seconds. Occasionally a fan that has stuck will break free on a restart. If it does, don’t assume you’re fixed. A fan that needed persuading is a fan on its way out, and you’re better booking a replacement on your terms than waiting for it to strand you.
2. Check the flue terminal from ground level. Anything obviously packed into it, a nest, ivy, drifted snow, is worth clearing if you can reach it safely from standing height.
3. Check your system pressure. It should read 1.0 to 1.5 bar on the gauge when the system is cold. Top up via the filling loop if it’s low. This won’t fix a C7, but low pressure can produce additional codes that muddy the picture, so it’s worth ruling out before the engineer arrives.
Do not remove the casing, do not try to spin the fan by hand, and do not work at height to inspect a flue.
When should I call a Gas Safe engineer?
Straight away, in practical terms. C7 is one of the few codes where we’d say don’t bother with more than one reset. The fan either turns or it doesn’t, and if it doesn’t, no amount of resetting changes that.
Call urgently if you also notice black staining around the flue outlet, or if anyone in the property has been feeling unwell when the heating runs. If you suspect combustion gases are entering the house, leave the property and call 0800 111 999. A working carbon monoxide alarm should be standard in any home with a gas appliance.
What will the engineer do?
- Read the fault history from the boiler to see whether C7 has occurred before and how often.
- Check for mains voltage arriving at the fan connector, which immediately separates a fan fault from a PCB or wiring fault.
- Test the fan motor itself, including resistance readings and bearing condition.
- Inspect the wiring harness and connectors for corrosion or damage.
- Check the flue and air intake for any restriction severe enough to stall the fan.
- Run a combustion analysis after the repair and record the readings on your paperwork.
Step two is the one that saves money. If the fan is getting power and still not turning, it’s the fan. If no power is arriving, the fan is fine and the problem is upstream, which is a different and sometimes cheaper repair.
How much does it cost to fix a C7 fault in Scotland?
Most C7 repairs land between £280 and £480, because a fan replacement is the usual answer. Guide prices for Scotland in 2026, parts fitted.
| Fix | Guide cost | Time on site | Notes |
|---|---|---|---|
| Diagnostic visit | £70–£130 | 45–90 mins | Usually deducted from the repair |
| Fan replacement | £280–£480 | 1.5–2.5 hours | The most common outcome by a distance |
| Wiring harness repair or replacement | £150–£300 | 1–2 hours | If the fan itself tests fine |
| Connector repair | £110–£190 | 1 hour | Corroded plug rather than failed loom |
| Air pressure switch | £180–£280 | 1–1.5 hours | Older models only |
| PCB replacement | £350–£650 | 2–3 hours | Where the board isn’t powering the fan |
| Flue clearing | £90–£180 | 30–60 mins | More with access equipment |
Fan prices vary by model. Fans for current Greenstar ranges are readily available. Fans for discontinued models from the early 2010s are harder to source and cost more, which is worth factoring in if your boiler is that generation.
Will my Worcester guarantee cover it?
Yes, if the boiler is within its guarantee period and your annual servicing is up to date. A fan is a boiler component, which is squarely what a manufacturer guarantee covers. Worcester Bosch guarantees run up to 10 or 12 years on Greenstar models when installed by an accredited installer and registered correctly.
The thing that trips people up is servicing. Most manufacturer guarantees require an annual service by a registered engineer, and a gap in that record can invalidate the cover. Find your service paperwork before you make the call, because it decides who pays for a £400 repair.
Is it worth repairing, or replacing the boiler?
Repair if the boiler is under ten years old. A fan replacement on a modern Greenstar is a sensible, well-priced job that should give you another decade of service.
Compare against a replacement quote once the boiler is past twelve years old, especially if parts availability is starting to look thin. A £450 fan on a fifteen-year-old boiler is money spent on one component while the gas valve, PCB and heat exchanger sit at the same age with the same wear. That’s not an argument for replacing a sound boiler, but it is an argument for getting both prices before deciding.
How do I stop C7 coming back?
- Book the annual service, ideally in late summer. An engineer can feel a bearing that’s on its way out, and catching it in August is far better than discovering it in December.
- Don’t leave the boiler completely idle over summer. Regular hot water use keeps the fan turning.
- Deal with new noises immediately. Humming, whining or rattling from the boiler is the fan telling you it has months, not years.
- Keep the flue terminal clear of leaves, moss and vegetation.
- Improve ventilation if the boiler is in a damp garage or outhouse. Reducing humidity slows corrosion in the fan housing and connectors.
What’s the Difference Between the Worcester C7 and EA Codes?
They sit in different parts of the boiler. C7 is a fan fault — the boiler can’t confirm the fan is running before it will even attempt to fire. The Worcester EA fault code comes later in the sequence: the fan has passed its checks, but the burner failed to ignite or the flame dropped out. A stuck C7 fault can sometimes stop the boiler getting as far as an EA attempt at all.
The bottom line
C7 means the fan has stopped, and the boiler won’t fire without it. One reset is worth trying, but if the fan doesn’t come back you need a Gas Safe registered engineer, and a fan replacement is the most likely outcome. If you’re reading this in September or October and your heating has just gone back on for the season, you’re in very familiar territory for us.
Need a fan replaced? Edinburgh Boiler Company covers Edinburgh, the Lothians and central Scotland with Gas Safe registered engineers, full combustion testing on every repair, and written pricing before any work begins.
This guide is general advice. Refer to your specific Worcester Bosch model’s user manual for reset instructions, and never remove the boiler casing or work at height to inspect a flue. Gas work must be carried out by a Gas Safe registered engineer.
