AVG PTR15-1000 Pressure Temperature Relief Valve 1000 KPA 15mm 1/2" BSP 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. High pressure may cause excessive discharge and possible premature failure of the operating relief valve (see table). The maximum water pressure usually occurs during the night, at the time of lowest water usage. In any mains pressure water heater installation if the water pressure exceeds 80% of the nominal set pressure of the operating relief valve, a Pressure Limiting Valve must be fitted to the cold inlet. If a cold water expansion control valve is fitted it will have a lower set pressure than the PTR valve and therefore will be the main operating relief valve.