Worcester Bosch C7 216 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch C7 216 fault code mean?
Worcester Bosch boilers use a two-part fault code system: the letter-number prefix (C7) identifies the fault category, while the three-digit suffix (216) pinpoints the specific cause. C7 covers fan-related faults — situations where the boiler's flue fan is not operating as expected during the startup sequence. Sub-code 216 is most precisely attributed to fan speed that is too low, with some sources noting it can also indicate fan speed that is excessive depending on the model variant. Either way, the boiler detects that the fan is not running within its required speed range and shuts down before ignition to prevent unsafe operation. The fan is a safety-critical component: it expels combustion gases through the flue and creates the correct airflow conditions for the burner to fire. Without confirmed fan operation, the boiler will not attempt ignition, leaving you with no heating and no hot water until the fault is resolved.
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 worn fan motor Common
The fan motor is the most likely culprit, particularly on boilers that are several years old. Worn bearings, a damaged shaft, or a motor winding failure can prevent the fan from reaching or maintaining the speed the boiler expects. The motor may turn sluggishly, make a humming or grinding noise, or fail to start at all.
- Loose or damaged fan wiring harness Common
The wiring loom and plug connectors between the fan and the PCB can work loose over time due to vibration, heat cycling, or corrosion. A poor connection disrupts the speed signal sent back to the control board, causing the boiler to read an incorrect fan speed and lock out even when the fan itself is physically fine. Engineers routinely check harness continuity and connector condition first before condemning the fan.
- Blocked or obstructed flue Sometimes
A partially blocked flue creates back-pressure that makes the fan work harder but appear to run slowly relative to its load, or can physically restrict the impeller. Common causes include nesting birds, leaves and debris entering a vertical flue without a guard, or ice forming around the terminal in winter. Check externally for any visible obstruction at the flue outlet.
- Faulty PCB Sometimes
The printed circuit board controls the fan drive signal and monitors the speed feedback. If the PCB is sending the wrong voltage to the fan motor, or is misreading the tachometer signal coming back from the fan, the boiler may report C7 216 even when the fan and wiring are in good condition. PCB faults are less common but more expensive to resolve.
- Moisture or condensate ingress Rare
Water finding its way into the fan motor or impeller housing — whether from a blocked condensate trap, a frozen condensate pipe, or a flue seal leak — can cause the impeller to jam or the motor windings to short. A frozen condensate pipe is worth checking in cold weather as a first step, since it can cause several secondary faults including fan-related lockouts.
How to fix it
- Check whether the gas supply is working DIY safe
Confirm your gas meter is on and that other gas appliances in the home (such as a hob or gas fire) are working normally. If there is no gas supply, contact your gas supplier rather than an engineer.
- Inspect the external flue terminal for visible blockages DIY safe
Go outside and look at the flue outlet on the wall or roof. Check for debris, leaves, a bird nest, or ice around the terminal. Do not reach inside or probe the flue — just look. If there is an obvious external obstruction you can safely remove without touching the flue pipe itself, do so. If in doubt, leave it for an engineer.
- Check and top up boiler pressure if needed DIY safe
Look at the pressure gauge on the front of the boiler. It should read between 1.0 and 1.5 bar when the system is cold. If it is below 1.0 bar, top it up using the filling loop (usually a braided hose with a valve beneath the boiler). Consult your boiler manual for the correct procedure for your model. Do not overfill past 2.0 bar.
- Thaw a frozen condensate pipe if the weather is cold DIY safe
In freezing temperatures, the condensate pipe (typically a white or grey plastic pipe running from the boiler through an outside wall to a drain) can freeze solid. Gently apply warm — not boiling — water to the external section of the pipe using a hot water bottle or cloth. Once thawed, attempt a reset. This step only applies when outdoor temperatures are at or below freezing.
- Attempt a single boiler reset DIY safe
Press and hold the reset button on your boiler (refer to your model's manual for its exact location and method) for the required duration. Allow the boiler to complete its startup sequence and monitor whether C7 216 reappears. If the fault clears and stays clear, monitor the boiler over the next hour. If the code returns immediately or comes back within a short time, do not reset again — repeated resets will not fix the underlying problem and can mask a developing fault.
- Call a Gas Safe registered engineer to diagnose the fan and wiring Gas Safe engineer
An engineer will use a multimeter to test voltage supply to the fan motor, check continuity of the wiring harness, inspect connectors for corrosion or poor contact, and measure the fan speed signal returning to the PCB. In many cases, a loose connector or a short section of damaged cable is found to be the cause and can be remedied quickly.
- Fan motor replacement if testing confirms motor failure Gas Safe engineer
If electrical testing points to the fan motor itself, the engineer will source the correct replacement fan assembly for your boiler model and fit it, checking speed operation before closing up the boiler. Fan replacements on Worcester Bosch boilers are typically completed within a single visit.
- PCB investigation and replacement if required Gas Safe engineer
If the fan and wiring both test as serviceable, the engineer will assess whether the PCB is sending or reading signals incorrectly. PCB replacement is a last resort and is more expensive — your engineer should advise whether the cost is justified given the age and overall condition of the boiler.
Parts you may need
- Flue fan assembly (Worcester Bosch compatible) · from £130
- Fan wiring harness / loom · from £35
- Fan connector plug and terminals · from £12
- PCB (printed circuit board) · from £280
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–£375, depending on the underlying cause.
Frequently asked questions
Is C7 216 always about fan speed being too low, or can it mean the fan is running too fast?
There is a genuine discrepancy between sources on sub-code 216. The most detailed technical listing attributes C7 216 specifically to fan speed being too low, with the recommended first check being the fan harness and connector. However, a small number of sources associate the same sub-code with excessive fan speed on certain model variants. If you are unsure which applies to your boiler, check your specific model's manual or ask the attending Gas Safe engineer to confirm — the diagnostic approach (test fan, wiring, and PCB) is broadly the same either way.
Can I keep resetting the boiler to get heat while I wait for an engineer?
You can attempt one reset to see whether the fault clears, but if C7 216 returns you should not keep cycling through resets. The fan is a safety-critical component that removes combustion gases from your home — operating the boiler when the fan is not working correctly carries a risk of carbon monoxide build-up. Switch the boiler off and arrange for a Gas Safe engineer to attend as soon as possible.
How much does it cost to replace a fan on a Worcester Bosch boiler?
A fan replacement including parts and labour typically costs between £225 and £375 in the UK, depending on your boiler model, your location, and the engineer's call-out rate. The fan unit itself usually costs £100–£200, with the remainder covering labour. If the PCB also needs replacing, costs can rise to £400–£600 or more — at which point, for an older boiler, your engineer may recommend weighing up replacement rather than repair.
My boiler is making a humming noise before showing C7 216 — what does that mean?
A humming sound before lockout often suggests the fan motor is trying to start but is struggling — possibly due to worn bearings, a seized impeller, or insufficient voltage reaching the motor. It is a useful clue for the engineer that the fault is likely mechanical (the motor or impeller) rather than purely electrical (wiring or PCB). Do not attempt to open the boiler casing to investigate — leave this for a Gas Safe registered engineer.