The Vaillant O-ring, washer, and gasket are used in various sections within your heating system. They are used when joining pipework to different parts within your central heating system. Heat exchangers, condensate traps, and many other parts require O-rings, washers, and gaskets. This part also fits the following: VAILLANT ecoTEC plus 612 (2005-2005) VAILLANT ecoTEC plus 612.