does water heaters drain thru the pressure valve
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.