I always drink honeyd water and noticed cold water becomes "sweeter" than warm (boiled) water with the same amount of honey applied.

I thought it's because of the lime, but what exactly happens when water is boiled?

It might be that some of the sweet compounds in honey are broken down somewhat (hydrolysis?) in hot water. Another thing may be that boiled water contains less impurities (air/oxygen is driven out, calcium bicarbonate is partly precipitated as calcium carbonate). Although these are just subtle effects, it might be that it does affect the taste considerably. The human sense of taste is very sensitive to changes.

 

But, I must admit, these are just my thinkings about the subject. Maybe someone with more knowledge about the precise composition of honey can give more insights.