Originally Posted by bubbles
Don't know what water heater you have but the thermostat you picture would be the 120 volt thermostat for a suburban that has gas and electric heating. It uses the 2 black wires for the AC and the 2 red wires are for the DC thermostat as the diagram shows. Both thermostats have the reset at the top. The DC and AC thermostats are different part numbers.
Correct. What the OP has pictured is the 120 volt hi/limit thermostat.
The 12 volt DC hi/limit thermostat is set up opposite.
As in this pic below, the 120 AC volt t'stat is on the left and the 12 volt DC t'stat is on the right.
If your water heater is propane ONLY, you would have the t'stat on the right.
You have to make sure you order and replace the correct one, as they are two different part numbers as explained by bubbles.