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
The boiler will refuse to fire until the triggering device is cleared. 🛠️ How to Fix the D6 Error 1. Check Connected External Devices viessmann d6 error
Check the gas supply
Clean or replace the ionisation/ignition electrode In technical terms, the D6 code signals a