This one (see attached photo) worked with no problem until I took it out of service about 20 years ago and replaced it with a conventional heater.  It has a huge copper coil inside.   It's been sitting in my basement every since. 
The label on the front says this:
              http://oldapplianceads.com/wp-content/uploads/2014/06/pittsburgh-automatic.jpg

Take a look at similar heaters on the web:
              http://www.ebay.com/bhp/antique-water-heater

Mine is probably over 100 years old.

Best offer.

-dk