Why does a condensing gas steam generator have a thermal efficiency higher than 1

 
The thermal efficiency of gas steam generator is converted by proportion, usually the thermal efficiency of gas steam generator is above 92%, and the thermal efficiency of gas condensing steam generator can be greater than 100%, or reach 109%. Maybe some friends can not understand, how can the thermal efficiency is greater than 100% it.
Condensing steam generator is another use of the heat in the flue gas to heat the water, theoretically the thermal efficiency of the condensing steam generator can reach a maximum of 110%, but this is only a theory of most of the steam generator manufacturers produce gas steam generator can reach 103% to 108%. This is why the gas steam generator thermal efficiency of more than 100%. It is also why you should choose a condensing gas steam generator.