Vaillant Condensate Trap (Page 3)

The condensate trap isolates the discharge which begins to build in the primary heating/cooling system. This is caused by the changes in the temperature and pressure within those systems. A discharge pipe connected to the condensate trap then allows any held water passage out of the property. The water inside a condensate trap can be mildy acidic due to carbon dioxide created by the boiler combustion dissolving in the water. That is why discharge pipes are made of plastic and not metal.