But these variations can cause large changes in CO concentration, which is one of the direct identifiers of incomplete (and therefore less efficient) combustion. These changes are also found in T2 values (thin azure line marked as temperature above the heat exchanger) that are tightly bound to the excess air ratio value. However, there is no major influence of the T2 temperature on the boiler’s operation (the desired outlet water temperature) because these fast temperature variations are well compensated by heat accumulation in the boiler.