A temperature and pressure relief valve, commonly called a T and P valve, is a vital part of every water-filled, heated tank in your home – a water boiler, a steam boiler, or even a domestic water tank connected to a boiler. Why?
The T and P valve prevents an explosion if water in the tank overheats. The valve, placed near the top of the tank, has a sensing tube that registers the water temperature and pressure. If the temperature or pressure get too high, the valve will open and safely drain water from the tank. You will notice a puddle on the floor near the drain tube from the T and P valve after it has opened.
A leak like this from the T and P valve indicates that either it needs to be replaced or the water pressure or temperature may be too high.
Without this safety device, water can become heated over the boiling point in the tank if it’s under pressure. If there is a break in the system, the water will immediately expand into steam with explosive force.