The escalators of August

So what’s worse than a 90 plus degree day in The District? How about walking up one of the long escalators at the Dupont Circle station’s south exit. On my way home and taking the down escalator I saw people walking up in the heat and actually felt bad for them. Both up escalators were not working.

It makes one wonder what takes an escalator off line? Are they that tempermental? I ask this because you often see them not working within the system. How old are the escalators in the Metro system? What would it cost to replace them all if they are too old?