Viessmann D6 Error Exclusive Jun 2026

In freezing weather, the plastic condensate pipe outside can freeze solid. The boiler detects this and blocks ignition to prevent damage.

In technical terms, the D6 code signals a "communication error" or a "short circuit" on the outdoor temperature sensor circuit. Viessmann boilers use weather compensation to adjust the flow temperature based on how cold it is outside. If the boiler cannot "see" the sensor, it doesn't know how hard it needs to work. Common triggers include: Damaged or frayed external wiring. Corroded sensor terminals due to moisture. A faulty outdoor temperature sensor. Internal PCB (Printed Circuit Board) communication lag. Immediate Troubleshooting Steps viessmann d6 error