If you're experiencing problems with your Rheem hot water tank, there are a number of troubleshooting options you can try before calling a plumber or shelling out hundreds of dollars for a new hot water system.
Gas Heaters - Gas Leak
If you have a gas heater, the first thing to check for is a gas leak. Step over to where you have the heater installed and take a good whiff. You should be able to detect a leak by smell. If you do pick up the scent of gas, do not try to fix it yourself. Call a professional right away.
Gas Heaters - Pilot Lights
Open the burner covers and check the pilot light. This is usually located at the bottom of a Rheem heater. If you don't see the pilot light going, try to relight it according to the models instructions. This usually requires turning the gas control knob to the "light" position and holding it there for a few seconds. Replace the burner covers and check again in half an hour. If the pilot light has gone out, you could have trouble with your thermocouple, the gas supply or a draft which is blowing out the flame. In any case, contact a qualified professional.
Electric Heaters - Testing The Circuit
The first thing to check with electric heaters is the main circuit breaker in the house. Identify the circuit that the water heater is on and make sure that this switch hasn't flipped. Next go to the hot water tank itself. There should be an electrical panel on the side with a dial. Check to make sure that the dial is set to the "heat" position. On some Rheem models, there will be a reset button. Press that. Wait about half an hour and try the hot water again.
Electric Heaters - Thermostat
This section should only be attempted by those who are experienced in working with electricity. On the hot water tank, open up the thermostat panel. You should see two wires connected here from the house main circuit. Using a voltmeter, test these leads to see if they are drawing current. If not, you have a bad thermostat and it needs to be replaced.
Electric Heaters - Heating Elements
In the majority of Rheem hot water tanks, two heating elements are present: an upper one and a lower. If you have current going to the tank and the thermostat works, you will need to pull out the heating elements and test each of these. First, drain the water from the tank. Then remove the upper heating element. Using your voltmeter, test the element for continuity. Then check the lower one. If one or both fail the continuity test, replace them.
Water leaks
Common to both electric and gas Rheem hot water tanks are water leaks. Check the Temperature Relief Valve on the side of the tank. If you find water dripping from here, consult the manual for your specific Rheem hot water tank to see what to do. Also check the pluming going into the tank and make sure the leaks aren't coming from here. If they are, you will have to replace the fittings. Lastly, look around the tank itself for evidence of water. If the Temperature Relief Valve and fittings are both OK, you might have a leak in the tank itself. Contact a professional to see what your options are.