BoilerFaultCodesViessmann 7E:1 Fault Code
Also written as 7E1 — same fault.
The Viessmann 7E:1 fault code means: your boiler system is communicating with multiple other boilers through a shared exhaust pipe, and it has detected a technical configuration error in that connection.. It appears on 5 Viessmann models in our database.
Technical description: With flue gas cascade
What causes the Viessmann 7E:1 fault?
This fault occurs when multiple boilers share a single chimney system and are failing to talk to each other correctly. It is usually caused by a poor wiring connection between the units or a conflict in the internal settings that tell each boiler which part it plays in the group. In some cases, a faulty electronic module or a blocked sensor in the exhaust pipe can also trigger this communication breakdown.
Engineer required
This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.
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Gas Safe Register →Viessmann models that show the 7E:1 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Viessmann 7E:1 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026