Worcester Bosch C6 216 Fault Code: Causes, Fixes & Repair Costs
What does the Worcester Bosch C6 216 fault code mean?
The C6 216 code means your Worcester Bosch boiler has detected that its fan is spinning more slowly than it should be. The fan plays a vital safety role — it expels combustion gases through the flue to the outside of your home — so when the boiler senses the fan speed has dropped below the expected threshold, it shuts down as a precaution rather than risk a dangerous build-up of fumes. You may also come across the closely related C6 215 code, which means the opposite: the boiler has detected the fan running too fast. Both sit under the C6 family of fan-related faults. C6 216 (fan too slow) is the more common of the two and is most often caused by a worn fan motor, a blockage in the flue terminal, or a clogged venturi inside the fan assembly. The boiler will not restart until the underlying problem is diagnosed and resolved.
General guidance only — not a substitute for professional advice, and not certified by a Gas Safe engineer. Always have your specific appliance assessed by a qualified professional. 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
- Blocked flue terminal Common
Debris such as leaves, compacted dirt, a wasp nest, or ice and snow can partially or fully block the flue outlet on the outside wall. When airflow through the flue is restricted, the fan struggles to reach its target speed and the boiler locks out. This is the most common trigger in autumn and winter.
- Worn or failing fan motor Common
Fan motor bearings gradually wear out over time, particularly on Greenstar i and CDi models manufactured between 2010 and 2016. As the bearings deteriorate, the motor loses torque and can no longer spin the impeller at the speed the boiler expects. This typically becomes apparent after 8–12 years of use.
- Blocked venturi or fan assembly Sometimes
The venturi is a small plastic throat inside the fan assembly that controls the air-to-gas mixture. If it becomes coated with dust, debris, or residue, the fan physically spins but cannot draw enough airflow — the boiler interprets this as insufficient fan speed. Cleaning or replacing the venturi usually resolves it.
- Loose or damaged wiring to the fan Sometimes
The connectors and cables between the fan motor and the PCB can work loose over time due to vibration, or become corroded or chafed. A poor connection means the PCB either misreads the fan speed signal or fails to deliver the correct voltage to drive the motor properly, triggering a C6 216 lockout.
- Faulty PCB Rare
The printed circuit board governs the fan speed signal and interprets the feedback it receives from the fan. If the PCB develops a fault — through age, water ingress, or a dry joint — it may incorrectly report low fan speed even when the fan itself is fine, or it may fail to drive the fan at all.
- Blocked or frozen condensate pipe Rare
While primarily associated with EA fault codes, a severely blocked or frozen condensate pipe can create back-pressure conditions that interfere with flue airflow, contributing to fan-speed-related shutdowns during cold weather.
How to fix it
- Check your gas supply is working DIY safe
Before anything else, confirm that other gas appliances in your home — your hob or gas fire, for example — are working normally. If you have no gas supply at all, contact your gas network provider rather than a boiler engineer.
- Inspect the outside flue terminal for visible blockages DIY safe
Go outside and look at the flue outlet on your external wall. If you can see leaves, ice, a bird or wasp nest, or any other debris blocking the grille, carefully clear it away — but only if you can reach it safely from ground level. Do not use a ladder, and do not poke anything inside the flue pipe itself.
- Check for a frozen or blocked condensate pipe DIY safe
During cold weather, locate your condensate pipe — usually a white or grey plastic pipe running from the boiler to an external drain or soil stack. If it feels solid with ice, you can thaw it gently using warm (not boiling) water poured over the pipe, or a warm damp cloth wrapped around it. Once thawed, attempt a reset.
- Reset the boiler once or twice DIY safe
Press and hold the reset button (often marked with a spanner or flame symbol) for around 5 seconds. If the boiler fires up and runs without returning the fault, it may have been a momentary glitch. However, if C6 216 reappears within a short time, stop resetting — repeated resets will not fix an underlying mechanical fault and can mask the problem for the engineer.
- Do not attempt to open the boiler casing or touch the fan Gas Safe engineer
Everything beyond the checks above involves removing the boiler casing, accessing the sealed combustion chamber, and working near gas-carrying components. This includes inspecting the fan, testing wiring, cleaning the venturi, or examining the PCB. These tasks must only be performed by a Gas Safe registered engineer.
- Call a Gas Safe registered engineer to diagnose and repair the fault Gas Safe engineer
A qualified engineer will inspect the fan harness and connectors, measure voltage at the motor terminals with a multimeter, check the impeller for smooth rotation, inspect the venturi for blockages, and assess the PCB signals. In most cases the fault is diagnosed and repaired in a single visit. Common outcomes are a fan motor replacement, venturi clean or swap, or a wiring repair. If the PCB is implicated, the engineer will advise whether repair or boiler replacement makes better financial sense given the age of the appliance.
Parts you may need
- Fan motor assembly (Worcester Bosch compatible) · from £120
- Venturi insert / air-gas manifold · from £35
- Fan wiring harness / connector set · from £25
- Printed circuit board (PCB) · from £220
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
Is C6 216 the same as C6 215 on a Worcester Bosch boiler?
No, though they are closely related. C6 215 means the boiler has detected the fan running faster than expected, while C6 216 means it has detected the fan running too slowly. Both fall under the C6 fan-fault family and both require a Gas Safe engineer to diagnose. C6 216 (too slow) is more frequently encountered and is most commonly linked to a worn fan motor or a blocked flue terminal.
Can I fix a Worcester Bosch C6 216 fault myself?
There are a couple of safe checks you can carry out — clearing visible debris from the outside flue grille, thawing a frozen condensate pipe, and performing one or two resets. However, anything beyond that involves opening the boiler casing and working near gas components, which must only be done by a Gas Safe registered engineer. Attempting internal repairs without the correct registration is illegal and dangerous.
How much does it typically cost to repair a C6 216 fault in the UK?
Most people pay somewhere between £150 and £380 all in, which covers the engineer's callout, diagnosis, and the most commonly replaced parts — usually the fan motor or venturi. Fan motor replacement on its own tends to come in around £230–£280 including labour. If the PCB turns out to be the root cause, the part alone can cost £200–£300 plus labour, which may push the total higher — at that point it is worth asking your engineer whether a new boiler represents better value, particularly if the appliance is over ten years old.
Why does my Worcester Bosch keep showing C6 216 after I reset it?
If the fault returns after one or two resets, there is an underlying mechanical or electrical issue that resetting cannot cure. Continuing to reset simply delays the proper repair and can occasionally mask the problem further. Switch the boiler off and call a Gas Safe engineer — the sooner the root cause is identified, the less risk of additional wear or damage to other components.
Could annual servicing have prevented my C6 216 fault?
Quite possibly, yes. During a service, a Gas Safe engineer checks fan operation, measures combustion performance, inspects flue integrity, and looks for early signs of motor wear or wiring degradation — all of which can flag a fan problem before it causes a breakdown. If your boiler is still within its Worcester Bosch warranty period and has a full service history with a Worcester Accredited Installer, the repair may also be covered under the warranty, so check before paying.