The Vaillant insulation is designed for the burner section of ecoTEC VU (condensing), ecoTEC VUW (condensing), Guernsey or Jersey only (condensing) and ecoTEC VUI (condensing) boilers. The burner produces heat in a combustible heating appliance. In natural gas appliances, gas is transferred to a gas valve and into the burner for ignition. The heat created is used to heat the water in the master heat exchanger.