Gaseous water (steam) has more volume than liquid water. Well, 100^C water will turn into steam, but will have more volume. The already put steam in the right chamber will conserve its volume. You will end up with 2 chambers full of steam, but one of the chambers will be of high pressure, it might even explode as well, as 1 liter of water equals 1500 liters of steam or sth.
I guess it would end up with the same volume of liquid water, only spread out between the two chambers. All the water being at a steady (i don't know the exact numbers so i'm just gonna say) 101 degrees, and all the steam being at a steady 99 degrees, both phases constantly outside their temperature range and in a perpetual state of transition. (because the steam would heat up a little when it transitioned to water, and the water would "absorb" some heat in order to transition to steam)