Junkers & Bosch Boiler Error E9, CE & C6: Meaning, Causes & Repair
Alongside the well-known EA flame-loss code, the three faults that cause the most winter emergencies on Junkers and Bosch boilers (Cerapur, Ceraclass, Euroline) are E9, C6 and CE. Here is what each code means.
Error E9: Safety Temperature Limiter (Overheating >105 °C)
Code E9 triggers when the primary heat exchanger overheats past 105 °C because boiling water cannot circulate—usually due to a seized circulation pump or a limescale-blocked plate heat exchanger.
Error C6 (Flue Fan / Air Pressure Switch) & Error CE (Low Pressure)
Code C6 indicates that the flue extractor fan or air pressure switch (presostato) is not detecting proper exhaust draft, whereas Code CE indicates heating circuit pressure has dropped below 0.7 bar.
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FAQ
Why does Error C6 appear during windy storms?
Strong wind gusts blowing directly into the exterior flue terminal can trip the differential air pressure switch, triggering a temporary C6 lockout.