Worcester Bosch C6 Fault Code Explained

If your Worcester Bosch boiler has flashed up a C6 fault, chances are the heating has cut out at the worst possible moment. It is a common code across Greenstar models, and understanding what it actually means can save you an anxious wait and a wasted call-out.

What does the C6 fault code mean?

C6 relates to the boiler's fan, or more specifically, the fan speed feedback signal. Every Worcester Bosch combi and system boiler uses a fan to draw air through the combustion process and push exhaust gases safely out through the flue. The control board expects to see a signal confirming the fan is spinning at the right speed. When that signal does not arrive, or arrives incorrectly, the boiler locks out with a C6 code as a safety precaution rather than risk incomplete combustion.

This is a lockout, not a display quirk. The boiler will not fire the burner until the fault clears, which means no heating and no hot water until it is resolved.

Common causes of a C6 fault

A few things typically sit behind this code:

• A faulty or failing fan that needs replacing
• A loose or damaged wiring connection between the fan and the PCB
• A blocked or restricted flue affecting airflow
• A fault on the printed circuit board (PCB) itself, though this is less common than a fan issue

Because the fan is a mechanical part with moving components, it is one of the more likely items to wear out over the life of a boiler, particularly on units that are approaching or past the 10 to 12 year mark. If you are already noticing other signs of age alongside this fault, our guide to signs you need a new boiler is worth a read before you spend money on repairs.

What to try before calling an engineer

You can safely attempt one reset. Most Greenstar models let you hold the reset button for a few seconds until the display changes. If the fault clears and stays clear, it may have been a one-off blip.

If C6 returns straight away or within a day or two, stop resetting it. Repeated resets do not fix a hardware fault and can mask a genuine safety issue with the flue or combustion process. This is not a job for DIY. Fan and PCB work sits squarely within Gas Safe registered engineer territory, and Worcester Bosch's own guidance is clear that only qualified engineers should open the casing.

You can check any engineer's credentials on the Gas Safe Register before they visit, which is a sensible five-minute check regardless of who you call.

Is a C6 fault covered by warranty or servicing?

If your boiler is still within its manufacturer warranty, a fan replacement is often covered, though you will usually need to use an approved engineer to keep the warranty valid. Check your paperwork or the Worcester Bosch website for your model's terms.

Regular servicing reduces the chance of fan faults developing unnoticed, since an engineer will check fan operation and flue condition annually. If it has been a while since your last service, our guide on how often a boiler should be serviced sets out what is reasonable.

When repair no longer makes sense

If your boiler is older, has thrown several different fault codes over the past year, or the fan has already been replaced once, it may be time to weigh up repair costs against a replacement. Our new boiler cost guide breaks down realistic pricing, and if you are unsure what size or type suits your home, what size boiler do I need is a good starting point.

Norvera covers the Midlands with fixed-price quotes and Gas Safe registered engineers, so if a C6 fault turns into a bigger conversation, you can get a fixed price without the runaround.

Need it fixed today?

A boiler with no heating in winter is not something to sit on. If you need someone out urgently, you can book an emergency callout rather than wait on hold with a large national provider.