Although a blocked gas line is one reason why the pilot light on a Rheem water heater won't light or stay lit, there are other reasons as well--some easier to correct than others. A faulty thermocouple or malfunction of the gas valve could be the culprit, but the problem may be as simple as a draft coming from a crack in the wall or under the door. Although Rheem recommends that you call a professional for any water heater repair, you can sometimes diagnose and correct the problem yourself.
Open the valve on the gas line by turning the handle until it is parallel to the gas pipe. Turn the gas control knob to the "Pilot" position and push it in. You should hear a faint hissing sound. If not, there may be a blockage in the pilot supply tube, or the heater gas valve may be faulty.
Turn off the gas, disconnect the pilot supply tube with a small wrench and clean it out with compressed air. If this doesn't correct the problem, you may need to clean or replace the gas valve; this is a job best done by a professional.
Light the pilot if you hear a hissing sound when you depress the gas control valve. If the flame starts but goes out immediately, check for drafts. If you can't find the source of a draft in the room, inspect the vent. It should extend 18 to 24 inches above the roof line and be free of obstructions. If the vent is too short, even a small breeze will blow the pilot out.
Adjust the thermocouple if the flame stays lit while you are holding the button down, but goes out when you release it. It is a small, bulb-shaped device located near the pilot aperture. When it is working properly, it generates a small electrical current to keep the gas valve opened when heated by the flame. A common problem with Rheem water heaters is a loose thermocouple that falls slightly out of position.
Replace the thermocouple if adjusting it has no effect. Turn off the gas, then disconnect the thermocouple, pilot tube, burner gas supply and pilot igniter from the gas valve and remove the sealed access door. When you replace these parts after purchasing a new thermocouple, you must install a new sealed access door to prevent the incursion of carbon monoxide into the home.
Contact your gas or propane supplier to have them inspect your service lines if none of these procedures works. The gas supply could be contaminated by water or oil that is restricting the gas flow.