This is a thermal question...
If one puts the bottom part of a double boiler on the stove, filled with water and then sets a sealed pressure cooker, with water in it, on top of it, can the temperature of the water in the pressure cooker exceed the temperature of the water in the lower pan?
Of course, all the usual standard ambient conditions apply and extraneous heat sources are ignored.
Had a little think about this one. Obviously, this is speculation on my part, since I'm not about to carry out an experiment.
How "filled with water" the bottom pan is, as well as how much it is heated would be important.
If the bottom pan is partially filled and heated to boiling point, creating steam, the latent heat stored within the steam will be transferred to the pressure cooker upon condensing, and thus the water within.
Since the pressure cooker is pressurised, this raises the boiling point of the water above 100 degrees, before evaporation occurs.
An example of how this raised boiling point is regularly utilised, is within the automobile cooling system. Typically pressurised to around a figure of 1 Bar, coolant temperature can reach figures of 105 - 110 degrees before overheating and bypass of the pressure cap occurs.
Normally though, the cooling fan is activated well below this point.
Or perhaps I'm way off. I'm sure someone else will confirm/correct this S.W.A.G.