This is the most likely culprit. The thermostat connects to the boiler via a 2-wire or 3-wire cable.
"Boiler model: Viessmann [model number]. Display shows error D6 (ignition/flame failure). I have reset once, confirmed gas supply is on, checked condensate and vents. Error persists. Please inspect ignition electrode, flame sensor, fan and gas valve." viessmann d6 error
The ionisation electrode sits next to the burner flame. It detects the heat and electrical conductivity of the fire to confirm a flame is present. Over time, this metal probe can develop carbon buildup, rust, or warp out of shape, preventing it from sending a clear signal to the control unit. 2. Defective Burner Control Unit This is the most likely culprit
If a technician recently changed service parameters (e.g., setting the boiler to work with an external weather compensator incorrectly), it can create a bus conflict. Display shows error D6 (ignition/flame failure)
The of your Viessmann boiler (e.g., Vitodens 100-W, 200-W)
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