Viessmann D6 Error [2021] -

This is the most likely culprit. The thermostat connects to the boiler via a 2-wire or 3-wire cable.

A: Some models store D6 as a history code without active lockout. Check your service menu. If boiler works fine, it may have been a one-time glitch. viessmann d6 error

: A safety device connected to the DE1 terminal has tripped. For example, if you have an external condensate pump with a safety switch, it might be blocked, triggering the D6 to prevent a flood. Configuration Glitches This is the most likely culprit

The of your Viessmann boiler (e.g., Vitodens 100-W, 200-W) If the error appeared after heavy rain or recent DIY work Whether you have heat and hot water right now it might be blocked