I think it's fine if you define efficiency by some other metric where it can rise above 100%, but if so you should clearly elucidate how.
At least in the US (not sure where you are), combustion boiler/furnace efficiency is required to be calculated using the HHV, which includes the heat of vaporization, not the LHV. The result is that even the highest efficiency condensing combustion heating systems all have rated efficiencies below 100%, which makes sense thermodynamically.
It seems that the standard in Europe is to instead calculate efficiency using LHV, resulting in the efficiency rating over 100% for condensing boiler. > 100% doesn't make sense thermodynamically, but is good enough for comparing when the same calculation is used.
Either way, it should be made more clear in the UI that it is using LHV.
If your audience is global, perhaps consider adding a toggle to switch the efficiency calculation to HHV. Think of it like the °C/°F toggle on some sites and apps.
Maybe you should educate yourself some before writing posts you know nothing about.
Except another commenter, obviously more versed in the field than I, specifically highlighted how this efficiency is calculated differently based on what is specified as the denominator, and the rules are apparently different for the US vs. Europe: https://news.ycombinator.com/item?id=40055464. So perhaps it is you that should educate yourself.