Temperature and pressure relief valves The temperature and pressure relief valve (T & P) is the primary "back-up" safety protection and a two-in-one safety device, which, as its name implies, responds both to excessive temperature and to excessive pressure in a water heater, which prevents the water in the pressurized hot water cylinder from overheating. For insure safe operation, the water heaters must be installed with temperature and pressure relief valves. The T&P valve responds to excessive temperature by expansion of the thermostat which lifts the disc off its seat and discharges overheated water, allowing cooler water to enter the tank and replace the discharged hot water in order to moderate the water temperature. When a valve is relieving water in volume, it is generally due to excessive temperature. The valve also responds to excessive pressure by discharging water to prevent further pressure increase. If a T&P valve is dripping, rather than relieving in volume, it usually indicates either thermal expansion or debris on the seat, which prevents the valve from closing tightly. Yuanben T&P relief valve for installation on unvented water heaters to prevent the temperature of water exceeding 100°C (212°F). Features: With pressed brass body. Coated ethylene-propylene diaphragm. Pressure setting: 10 bars max (150psi). Temperature setting: 93°/94°C. CQC approved. Mounting: A T&P relief valve is a mechanical device which, like any mechanical device, is subject to failure, particularly when tampered with or improperly installed, such as other safety valve, If the valve cannot do its job, the water in the tank may become superheated (over 212°F). So properly mounting T& P Valve is important.