There are two perfectly identical boilers containing the same amount of water, switched on and working in identical environments. Both are setup so that the heating starts when the temperature of the water falls to exactly (or, of course, initially is below) T1 degrees and stops when it raises to exactly T2 degrees, thus keeping the temperature of the water in range T1..T2. The only available indication is whether heating is in progress.
If in an instant moment of time only one of the boilers indicates heating in progress (i.e. the other is in state of no heating), what is more probable - its water is hotter or cooler than the other's, or the chances are equal?