valve is most often connected to a discharge pipe made of copper or plastic. This valve operates like the radiator cap on a car to relieve excessive temperature or pressure build up inside the tank if it approaches the limits of the tank’s safe design range. This valve is located on top of the tank and often is threaded directly into the tank top itself. To test the valve, lift up on the handle slightly and hot water should discharge out of the overflow pipe. It should not be leaking. If it is, it is time to replace the hot water heater immediately.
The in order to operate safely, the hot water heater must have a discharge line installed. The first photo illustrates a properly installed copper TPRV discharge line which routes to a floor drain. The second photo is of a hot water heater with no discharge line. Were the TPR valve to rupture, scalding hot water might spray outward from the valve and pose a safety hazard to occupants. It is very important that the valve have a discharge line attached, and that it be installed at a length sufficient to be no more than 6 inches off the floor. In addition, it should route to a floor drain or to the exterior if there is no drain. With out a drain, 40 to 50 gallons or water will have no place to go in the event of a discharge, and cause possible injury and water damage to contents.