BoilerFaultCodesViessmann CE Fault Code
The Viessmann CE fault code means: your boiler is having trouble communicating with an add-on control or an external smart home accessory, which may affect its ability to run efficiently.. It appears on 6 Viessmann models in our database.
Technical description: Control mode - Communication fault-ext. extension
What causes the Viessmann CE fault?
This fault occurs when the boiler's main control board loses the digital handshake with an external accessory, such as a smart home interface or an expansion module. The most common reason is a loose connection in the low-voltage wiring or a hardware failure within the add-on component itself. Without this communication link, the boiler can no longer receive instructions on how hard it needs to work to heat your home.
DIY fix possible
Check if any external smart thermostats or controllers are turned on and have battery power.Restart the boiler by turning the power off and back on at the fused spur switch.Ensure any wireless hubs or range extenders nearby are plugged in and working.
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Viessmann models that show the CE fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann CE fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
- Viessmann Vitodens 050-W BPJD manual (PDF)
- Viessmann Vitodens 100-W WB1A manual (PDF)
- Viessmann Vitodens 300-W manual (PDF)
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026