The relief valve temperature sensor measures temperature and pressure. The relief valve temperature sensor should be located in the hottest part of the tank, typically the top 6 inches. The sensing element should be immersed in the hottest water (at the top 6 inches of the tank).
Usually a dripping relief valve is the result of thermal expansion or foreign material at the seat preventing it to close. A valve that relieves in volume is usually due to excessive high temperature. A new temperature and pressure relief valve should be installed when a water heater is replaced. Alterations of parts may result in devastating damage or injuries.