Worcester Bosch C7 217 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch C7 217 fault code mean?
The C7 217 fault code appears when the boiler detects that the fan has stopped or behaved erratically during normal operation — specifically, the fan cuts out while the appliance is running rather than failing to start in the first place. Worcester Bosch uses a two-part code system: C7 identifies a fan-speed fault, while 217 pinpoints the trigger as the fan stopping mid-operation. The closely related C7 214 code, by contrast, means the fan never spins up at all during the start phase. Because the fan is responsible for expelling flue gases safely and creating the draught that allows ignition, the boiler locks out immediately when it detects the fan is no longer running correctly — this is a deliberate safety shutdown, not a catastrophic failure.
General guidance only — not a substitute for professional advice. Any gas work must be carried out by a Gas Safe registered engineer. If you smell gas or suspect carbon monoxide, leave the property and call the National Gas Emergency line on 0800 111 999.
Common causes
- Faulty or seized boiler fan Common
The fan itself is the most frequent culprit. Over time the fan motor bearings can wear, the impeller can crack or become unbalanced, or the motor windings can fail. Any of these will cause the fan to slow or stop mid-cycle, immediately triggering the C7 217 lockout. Unusual noises — humming, rattling, or a grinding sound — before lockout are a strong indicator that the fan is the source.
- Fan wiring harness or connector fault Common
The wiring loom that carries power and control signals to the fan can develop loose connections, corrosion, or chafed insulation. A poor connection may allow the fan to start but then drop out under load or vibration, producing an intermittent C7 217 fault that may temporarily clear on reset before returning.
- Blocked or obstructed flue Sometimes
A partial blockage in the flue system — caused by debris, a bird nest, or a damaged terminal — can put abnormal back-pressure on the fan, causing it to labour and ultimately stall. Worcester Bosch's diagnostics list restricted airflow as a potential cause of C7 faults. The fan itself may be in perfect condition; it simply cannot maintain speed against the restriction.
- Faulty PCB (printed circuit board) Sometimes
The PCB governs the fan's speed and receives feedback via the tacho signal wire. If the PCB stops sending the correct drive signal, or misreads the tacho feedback, it may cause the fan to run erratically or cut it out entirely — then log C7 217 as the result. PCB faults are less common but become more likely on older or water-damaged boilers.
How to fix it
- Reset the boiler once (twice at most) using the reset button as described in your user manual DIY safe
A single reset can clear a transient fault. Press and hold the reset button for about 3 seconds, then wait while the boiler attempts to restart. If the C7 217 returns immediately or after a very short run, do not keep resetting — repeated resets will not fix the underlying problem and could mask a safety issue.
- Check that the external flue terminal is free from visible obstructions DIY safe
Go outside and visually inspect the flue outlet on the external wall or roof. Look for leaves, spiders' webs, birds' nests, or any debris blocking the opening. Do not insert tools or fingers into the flue — if you can see a blockage you cannot easily remove by hand from the outside, leave it for an engineer.
- Verify boiler system pressure is between 1.0 and 1.5 bar DIY safe
Check the pressure gauge on the boiler fascia. If pressure has dropped below 1 bar, top it up via the filling loop following your boiler's user manual. Low pressure alone is unlikely to cause a C7 217, but ruling it out first avoids an unnecessary call-out.
- Listen for unusual noises from the boiler before or during lockout DIY safe
If it is safe to do so, switch the boiler on and listen carefully in the first few seconds. A humming, rattling, or grinding sound from inside the casing strongly suggests a failing fan motor or bearing. Note what you hear and report it to the engineer — this will speed up diagnosis.
- Do not open the boiler casing or touch any internal components Gas Safe engineer
The fan, its wiring harness, internal flue connections, and PCB are all inside the sealed casing. Tampering with any of these without the correct tools, training, and Gas Safe registration is dangerous and may invalidate your warranty.
- Have a Gas Safe registered engineer inspect and test the fan, harness, and PCB Gas Safe engineer
An engineer will use live electrical testing to check the fan motor's resistance, verify the tacho feedback signal, inspect the wiring harness for damage or poor connections, and carry out a flue integrity and airflow check internally. If the fan is faulty it will be replaced with a manufacturer-approved part. If the PCB is sending incorrect drive signals, it will be tested further and replaced if necessary. Always ask to see the engineer's Gas Safe ID card before work begins.
Parts you may need
- Boiler fan (Worcester Bosch compatible) · from £85
- Fan wiring harness / loom · from £30
- PCB (printed circuit board) · from £200
- Flue terminal / terminal guard · from £20
The exact spare depends on your boiler's GC number (on the data badge). Check this against the part before buying.
Typical repair cost
Expect to pay roughly £150–£380, depending on the underlying cause.
Frequently asked questions
What is the difference between a C7 214 and a C7 217 fault on a Worcester Bosch boiler?
Both codes indicate a fan problem, but they point to different stages of the fault. C7 214 means the fan failed to spin up at all during the start-up phase — the boiler never got going. C7 217 means the fan started normally but then stopped or ran at an irregular speed during actual operation. In practice, C7 217 can be slightly harder to diagnose because the fault is intermittent, but both codes usually point to the same culprits: a failing fan motor, wiring issues, or a flue obstruction.
Can I reset my Worcester Bosch boiler to clear the C7 217 fault?
Yes, one or two resets are worth trying. Occasionally a transient electrical glitch or brief draught disturbance will trigger the code and a reset will clear it permanently. However, if the fault returns after one or two resets you should stop and call an engineer. The boiler is locking out for a safety reason, and repeatedly resetting it without fixing the cause can delay a potentially serious issue being found.
How much does it cost to replace a fan on a Worcester Bosch boiler in the UK?
Most homeowners pay between £150 and £380 all in for a fan replacement, which covers the part and the engineer's labour. The exact cost depends on your boiler model and your location. If the PCB turns out to be the cause rather than the fan itself, parts and labour can push costs higher — typically £300 to £500 or more. For boilers over 10 years old it is worth getting a quote for a full replacement alongside the repair quote, as a new boiler may offer better long-term value.
Is the C7 217 fault dangerous — could it mean carbon monoxide is leaking?
The lockout itself is a safety feature designed to prevent dangerous situations. When the fan stops, the boiler shuts down before incomplete combustion or a build-up of flue gases can become a hazard. That said, you should take any boiler fault seriously. If you have a carbon monoxide alarm and it sounds, evacuate immediately and call the Gas Emergency Service on 0800 111 999. Do not use the boiler again until a Gas Safe engineer has confirmed it is safe.