: Turn off the power to the boiler for 30 seconds and then restart it. This can sometimes clear temporary communication glitches.
On Viessmann boilers (particularly Vitodens 100, 200, and 200-W models), the D6 code signals a fault during operation. The burner has started, but the ionization electrode (the boiler’s "flame sensor") isn’t detecting a consistent flame.
Even a small amount of trapped air can act as a blockage, preventing water from flowing freely. This is a very common cause of an intermittent D6 error that appears and then disappears.
Sometimes the spark is weak, or the ionization cable has high resistance. Look for cracked insulation, loose spade connectors, or burn marks on the ignition transformer. viessmann d6 error
2. On Viessmann Heat Pumps (Vitocal 111-S, 200-A, 222-S, etc.)
If you own a Viessmann boiler (particularly the Vitodens 100, 200, or 050-W series), seeing an error flash up on the digital display can be stressful—especially in the middle of winter. One of the most common fault codes reported by Viessmann owners is the .
On modern heat pump units, the D6 error changes context and points to a hardware protection mechanism: : Turn off the power to the boiler
A registered Viessmann technician or heating engineer will follow this logical path:
Here is everything you need to know to decode this digital hiccup and get your home feeling cozy again. What is Input DE1? Think of the EA1 module
Review recent maintenance or changes
: If thermostatic radiator valves across your rooms reach their target temperatures and close simultaneously, they strangle the system's overall water volume flow.
Before the boiler fires up, the control board checks the air pressure switch. The switch must be in the "open" position when the fan is off. If the control board detects that the switch is stuck "closed" before the fan even starts, it triggers the D6 error and locks down the boiler for safety. Primary Causes of the D6 Fault
If the pressure is fine and a reset doesn't work, the issue is likely internal. A Viessmann Trained Installer or Gas Safe engineer will need to: Installation Instructions - Flow Sensor - Viessmann US The burner has started, but the ionization electrode