Viessmann Vitoladens 300-C Installation And Service Instructions Manual page 42

Commissioning, inspection, maintenance
Cleaning the heating surfaces
Fig. 38
42
(cont.)
3. Clean the trap.
4. Refit the trap, condensate hose and neutralising
system.
Fill the trap with water.
Danger
If the trap is not full, flue gas can escape.
Escaping flue gas can cause life threatening
carbon monoxide poisoning. Always fill the
trap with water before commissioning.