Vaillant 178973 domestic hot water heat exchanger

A Vaillant 20 plate heat exchanger suitable for ecoTEC VUW (condensing) boilers. The heat exchanger transfers heat from a boiler's burner to water. A primary heat exchanger is found in all boilers, using heat from a burner to raise the temperature of the water in the system while a secondary heat exchanger is present only in combis and allows the heat to be transferred between closed systems.