Error C6

Safety first:

1) If you smell gas, suspect a carbon monoxide issue (headaches, nausea, dizziness, flu-like symptoms), or see water streaming from the boiler, leave the property immediately and contact the gas emergency service and/or emergency services. Do not attempt to use the boiler. Open windows for ventilation if safe to do so.

2) Do not attempt internal electrical or gas repairs unless you are a qualified Gas Safe registered engineer. Isolate the electrical supply at the boiler isolator before opening the casing for any inspection, and only do visual checks that do not require altering gas or sealed parts.

Initial homeowner checks (safe, non-invasive):

1) Record the exact error code and sequence shown (e.g. C6, any sub-code like 215/216 if displayed), the boiler model and serial number, and the circumstances when the code appeared (e.g. after a power cut, during use, after a freeze). Take a photo of the display for the engineer.

2) Try a single reset using the boiler reset button. If the fault clears and does not return, monitor the boiler closely and book a service. If the fault returns, stop resetting repeatedly.

3) Listen and observe when you press reset: do you hear the fan start-up (a brief whirring sound) before the lockout? If the fan does not start at all, that’s a strong sign of a fan motor, wiring, or control fault.

4) Check the external flue terminal on the outside wall for obvious blockages (nests, debris, leaves, snow/ice) and clear only loose debris from the outside. Do not insert tools into the flue. Ensure nothing is blocking the terminal or the surrounding area.

5) Check visible condensate pipe runs (usually from boiler to outside) for freezing or blockage. In cold weather, a frozen condensate pipe can cause pressure and drainage problems that affect operation.

6) Look inside the boiler only if comfortable and competent: with the electrical supply off at the isolator and the front panel removed, look for obvious water ingress, corrosion, loose connectors at the fan harness, or burnt wiring. Do not touch live parts.

Diagnostic steps that require competence or an engineer:

1) If you are technically competent and qualified to work safely on electrical systems, you can isolate power, remove the front panel and check that the fan impeller turns freely by hand (with power disconnected). Stiff or seized bearings indicate fan replacement is required. Do not attempt to run the fan by hand with power applied.

2) A competent person can check continuity of the fan cable and measure supply voltage to the fan during a start attempt using a multimeter or clamp meter. Low or no voltage from the PCB to the fan indicates a control/PCB issue; correct voltage but no fan movement indicates a failed fan motor.

3) The air pressure switch and its tubing should be inspected for blockages, split tubing, or moisture. A failed pressure switch can give incorrect fan speed/flow readings. Testing or replacing this component is a job for an engineer.

4) If fan wiring, connectors, impeller damage, or PCB faults are suspected, these parts are usually replaced rather than repaired. Fan bearings can sometimes be replaced, but due to labour and cost most engineers will fit a new fan assembly.

When to call a professional:

1) Call a Gas Safe registered engineer whenever the fault does not clear after the simple non-invasive checks (reset, exterior flue check, condensate check). Fan motor replacement, electrical tests, PCB replacement, or pressure switch repair must be carried out by a qualified engineer.

2) If you find water inside the boiler, significant corrosion, or if the fan appears damaged or seized, isolate the appliance and arrange an engineer visit.

3) Provide the engineer with the recorded fault code(s), photos, and details of what you already checked — this speeds diagnosis and helps them bring the correct parts.

Final notes:

- Treat C6 as a safety-related fault. It is acceptable to perform basic external and visual checks yourself, but do not carry out gas, sealed-system, or live electrical repairs.

- Avoid repeated resets — if the fault reappears, isolate the boiler and call a Gas Safe engineer to diagnose and fix the root cause.

- If you are unsure at any point or suspect carbon monoxide exposure or a gas leak, evacuate and call the emergency services immediately.