What the manual says
Manufacturer manualWhilst filling is in progress (weather-compensated control unit)
From this model's manual
Verified against the Viessmann Vitodens 222 F installation & service manual.
DIY fix possible
Locate the filling loop (a flexible silver hose) underneath your boiler or near your pipework.Gradually open the valves on the filling loop to allow water into the system.Monitor the pressure gauge on the front of the boiler until it reaches the green zone (typically between 1.0 and 1.5 bar).Close both valves firmly once the pressure is correct.
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