There are two kinds of heat exchanger that can be installed, they are 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 between one closed system and another.
We recommend that all parts are fitted by a fully qualified gas safe certified plumber.