Hot Water Expansion PTR Valve 15mm Blue 850KPAThe Pressure and Temperature Relief valve (PTR) is designed to relieve the increase in pressure caused by water expansion during the normal heating cycle. The valve will then relieve the increase in pressure by releasing drips of hot water to the drain line. Should the electrical temperature cut-out device cease to operate correctly, the water will overheat. The temperature probe will then open the PTR valve and discharge hot water to the drain line. It is recommended that an ECV be fitted to the cold water supply line. This will relieve cold water, not hot water, during the heating cycle, saving energy and increasing the life of the PTR. Some local governments make it mandatory to install an ECV in the cold water line. PTR and ECV valves are safety valves and should be replaced every 4 years.