A drain valve is a convenience feature on a water heater. The only time it will be used is when draining for repairs, when it is being discarded or when flushing the lime scale out with a hose. If there is no lime, calcium or iron buildup in the water heater, the water will drain easily from the valve. However, if there is buildup, chunks of it can jam the opening and impede the flow of water to such an extent that it won't drain at all. Determine whether or not the valve is actually clogged. Turn off the water heater at the breaker panel. Alternatively, turn the gas valve until the valve sits perpendicular along the gas pipe. Attach a drain hose if the drain valve is not within close proximity to a drain. Open the drain valve and begin to drain the tank. Open the pressure-relief valve on top of the water heater. Alternatively, turn on a hot water faucet. This will eliminate the negative pressure in the tank and allow it to drain. If the drain begins to run clean and clear, the problem is solved. If the water still trickles out, the valve is clogged. Step firmly onto the drain hose, about 2 feet from the water tank. This will force an air bubble back into the tank and will temporarily unclog the valve if there is a lime scale or other debris-related clog. The clog may promptly return after a few minutes if the tank is full of debris. Repeatedly stepping on the hose and forcing air back into the tank after each clogging episode will eventually drain the tank, but it may take more time to do this than it is worth. Back-flush the water heater. Turn off the valve and attach a faucet to the drain hose. Use a two-sided female coupling washer hose for this task. A washer hose will thread onto the end of a drain hose and it will also thread onto a standard garden faucet nozzle or a washtub faucet. Once the washer hose is attached to a faucet and the drain hose, turn the faucet on and allow pressure to build up into the hose. Turn on the drain valve to allow the pressure from the hose to flow into the water tank and unblock any deposits in the valve. Turn the valve off and unscrew the hose from the drain. Turn the valve back on to let the water drain. If the water does not drain, the lime buildup may be too severe or the valve may be defective. Remove the drain valve from the water heater. Allow the tank to cool for 24 hours before attempting this. Place a pipe wrench into the drain valve body and turn it off slowly. As you unscrew it, the fixture may begin to leak profusely, but the leaks may quickly clog with lime particles. When the valve is completely off, expect a rush of water to pour out of the hole. This may continue to drain the water tank successfully. However, the draining may also stop quickly if the lime deposits are severe and clog the drain hole. Insert a screwdriver into the drain hole from which the valve has been removed. Swirl the screwdriver around and pull it out. The water will begin to drain, but it also may plug back up quickly. Continue to insert the screwdriver through the hole as necessary to break up the clog before the tank has completely drained. Things You Will NeedWear a pair of leather-palm gloves to protect your hands from hot water when removing the drain valve.