Six months ago, I had problems with the left front brakes, caliper was sticking so it was replaced. All go since. Last week I notice the wheel and caliper behind it is hotter at times compared to the right one, this gets warm, the rears are cold. Brakes are working fine and no alarms up on the dash, 

It could be that the other side is slightly sticking and therefore not being used as effectively as the other side (replaced caliper side) and is colder as a result of this?

The rears are not normally running anywhere near as hot as the front (unless fully loaded vehicle)