The Vaillant part is located within the heat exchanger section. There are two kinds of heat exchangers that can be installed, the primary heat exchanger and the secondary heat exchanger. The primary is present in almost all boilers and it allows the transfer of heat from the burner to the water within the system. The secondary heat exchanger is only required in a combi boiler and allows the heat to be transferred from one closed system to another.

Brand Name	Vaillant