Cool Mike wrote:

The thermostat is electronic and is set at the proper temperature (hot). Has the PT (Pressure temperature) safety valve ever opened and let hot water out? Its the brass valve with a small Handel on the top, like at home.
They do run hot, this is to give you as much hot water as possible with only 6 gal in storage.
When you light off the heater, you should have the pump off and the hot water valve in the kitchen sink open, to let water drip as it heats and expands. Or you can open the PT valve before you turn it on to let some water out, and air in to the top of the tank, to allow for expansion.
If that PT valve starts dripping, replace it, and never put a pipe plug in its outlet.
If your new to RVing, Camping World has some good books on all of this stuff.
Good Luck, and happy camping.