Originally Posted by wmtire
X2 on Ron's advice.
A lot of people will add an inside electric heating element switch for the Suburban water heaters, since most do not come equipped that way. There are several forum threads explaining this. Many of these people basically wire the inside switch so it controls the 120 volt outlet the water heater is plugged into. They leave the outside switch turned on, and just control the outlet plug with the inside switch. There are also other ways to do it too.
I would check the inside switch for the electric heating element and make sure it is even connected to anything. It's possible they used a control panel with an inside switch but didn't even wire it for an inside switch.
Now that's very possible that it has a switch on a panel they put in every unit but isn't functional.