You have water heater with two elements.
Two-element water heaters are 240Volts.
1) Lets talk about what makes a 240Volt circuit
See basic water heater circuit:http://waterheatertimer.org/B220C.html
Open link, and illustration at top of page is your water heater circuit
Notice that two insulated wires come from the circuit breaker and go to the water heater.
These two wires are 120volt each. When these two 120Volt wires combine, they create 240Volts
These are called hot wires because they come from the hot busbars.
There is also a bare copper wire that comes from neutral busbar.
The bare copper wire is a safeguard, and is not necessary for the 240V circuit to work.
Inside each circuit breaker box is 1 neutral busbar, and 2 hot busbars.
Open image below, and it shows typical residential breaker boxhttp://waterheatertimer.org/images/Inside-Main-Breaker-Box-420.jpg
In a residential home, each circuit takes two wires to complete the circuit.
For 120Volt circuit, you need 1 neutral wire and 1 hot wire to complete the circuit. These are usually a black and white wire. The bare copper wire is a safeguard.
For 240Volt circuit, you need 2 hot wires to complete the circuit, and each hot wire comes off a different busbar. These can be a black and white wire, and sometimes a black and red wire. The bare copper wire is a safeguard.
With a 240Volt water heater the two hot wires connect to the black and red wires located on top of water heater.
2) Let's talk about wiring inside a water heater.http://waterheatertimer.org/images/WH-w-combined-530.jpg
Open image on link above, and it shows your 240volt water heater wiring.
The 2 hot wires from breaker box connect to the red and black wires on top of heater.
Inside each water heater, the wires are color-coded and will appear the same, or nearly the same, as shown on link above.
As long as your wiring appears like the image, and the hot wires from breaker box connect correctly, and the circuit breaker is working fine, then your water heater will work.
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3) More electric water heater links about water heaters, thermostats and tank wiring:http://waterheatertimer.org/How-electric-water-heater-works.htmlhttp://waterheatertimer.org/How-water-heater-thermostat-works.htmlhttp://waterheatertimer.org/How-to-wire-water-heater-thermostats.html