There are two switches to be concerned about.
There should be a red residential looking switch inside your rig somewhere. It should illuminate when turned on.
There should also be a rocker switch on the water heater itself. Remove the outside access panel to find the switch.
Also make sure the breaker for the water heater is not tripped.
There is also a chance that the water heater element is shot.
Check out the water heater guide in the "Tools" area. That can be found at the top tool bar of each forum page.
Here is a link to the Suburban water heater guide. [
LINK]
Peace
Dave