Viessmann Vitodens 100-W fault codes

5 codes from the Viessmann manual for the Vitodens 100-W gas boiler. Pick one for what it means, the likely causes and where to start.

Code	What it means
416	Flue gas temperature sensor placement fault during commissioning
694	Burner in a fault state, signal comparison deviation, flue gas high limit safety cut-out
799	No DHW heating, no central heating, central heating circuit pump electrical fault
980	No DHW heating (minimum system pressure too low before start)
981	No DHW heating (minimum system pressure too low during DHW heating)