The pressure temperature relief valve (PTR) is an expansion valve that is situated on the outside of hot water services. It has a sensor probe inside the hot water service that reacts to the increase of temperature inside the tank. Should there be a fault with the appliance that causes the water to overheat, this valve will expand allowing water to pass. This will relieve excessive pressure within the appliance and protect it from exploding. These valves can also be activated manually by pulling the handle.
It is a requirement that the drain lines running off the PTR valve discharge in a safe location. This is to protect the occupants from burns and scolds. PTR lines can release boiling water at any point in time without warning. If an occupant has a problem with their hot water unit and is trying to troubleshoot the issue, they will be standing in close proximity to the appliance. Should they manually pull this valve there is a possibility they will be burned.
It is recommended by manufacturers that PTR valves be opened every 6 months to let water pass. This is to ensure they are operational as well as to re-lubricate the internal mechanical components of the valve. Again, if these lines are not run to a safe location, the operator may burn or scold themselves.