Viessmann D6 Error

On Viessmann boilers (particularly Vitodens 100, 200, and 200-W models), the D6 code signals a "flame signal missing" fault during operation. The burner has started, but the ionization electrode (the boiler’s "flame sensor") isn’t detecting a consistent flame.

The sequence usually looks like this:

This is not the same as an F4 code (no ignition at all). D6 means the flame was there but disappeared or wasn’t recognized. viessmann d6 error

If the above steps do not resolve the D6 error after 15 minutes of runtime, do not keep resetting the boiler. The issue is likely a failed BCU or display module, requiring a Gas Safe registered engineer (UK) or licensed HVAC technician (US/Canada). On Viessmann boilers (particularly Vitodens 100, 200, and

If your Viessmann boiler is showing a D6 error, it usually indicates a flame failure or ignition problem. That can mean the burner is not lighting, the flame is being lost during operation, or the ignition sequence is interrupted. Below is a concise guide to diagnosing, troubleshooting, and when to call a pro. This is not the same as an F4 code (no ignition at all)

Go outside and find the white plastic pipe coming from the boiler. If it’s frozen:

After clearing, reset the boiler. If the error clears, you’ve solved it.