Worcester Bosch [C6 224] fault codewhat it means and how to fix it

The fan on a condensing boiler both supplies combustion air and clears flue gases, and the control board monitors its actual speed against the commanded speed on every cycle. C6 224 means the two do not agree. The boiler will not fire when it cannot verify that flue products are being removed, which is exactly the behaviour you want. The usual physical cause is a fan reaching the end of its service life, and it normally warns you first with weeks of rattling or droning on startup. The alternative cause — a restricted flue or air intake — produces an identical reading and carries a genuine combustion risk, which is why the flue is always checked as part of diagnosing this code.

1. 1

   Look at the flue terminal outside. Check for nests, leaves, or anything built near it since the boiler last worked — a new fence panel or shed roof is enough.

   Look only. Never push anything into a flue terminal; you risk driving a clearable obstruction deeper into the flue.
2. 2

   Listen at startup. Rattling, droning or grinding before the lockout means worn bearings, and telling the engineer that saves them diagnostic time.

3. 3

   Reset once. If it returns within a cycle or two, leave it and book someone.