A stuck pump, airlock, or blocked filter can cause the flow switch to trigger a D6 error because water isn't moving through the heat exchanger fast enough.
If your boiler was recently serviced or installed, a technician might have accidentally changed a "coding address" in the service menu that doesn't match your system's actual hardware. viessmann d6 error
: A faulty or disconnected sensor (such as the outdoor temperature sensor or a flow sensor) sending an "open circuit" signal to the control unit. A stuck pump, airlock, or blocked filter can
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 If the pressure is fine and a reset
This is a digital input configured to monitor external safety loops or conditional commands.