Your water heater works with heat and pressure; the temperature pressure relief valve is designed to keep your tank from exploding if either of them exceed safe limits. The temperature pressure relief (TPR) valve is the main safety feature in every tank-style water heater.
When water is heated, it expands and creates more water volume; this volume creates more pressure in a closed system, such as a tank. In the past, valves were installed that only released the pressure on tanks, but they didn’t deal with the other problem–temperature.
Two conditions contribute to water heater explosions: water temperature above the boiling point (212 degrees Fahrenheit) and unrelieved pressure. Water below 212 degrees that is under extreme pressure will simply find a crack or weak spot in the tank and leak, but it won’t cause the tank to explode. However, after the boiling point is reached, pressure can rise and water can expand in volume rapidly. If the tank’s pressure isn’t released quickly…boom. You’ve got a 40-gallon rocket on your hands that can cause serious damage to your home and injury to anyone who is unlucky enough to be in its path.
This is where the TPR valve comes in to save the day. The current industry standard setting for the TPR valve is to open at 210 degrees of water temperature and/or 150 psi of pressure. It simply doesn’t let pressure build up or water temperatures to reach the boiling point.
When either the temperature or the pressure becomes too high, the valve opens and releases hot water and pressure. The water that is released is replaced inside the tank with cooler water, which lowers the temperature and the pressure. The valve will then shut off once safe conditions are restored.
The TPR should be found within the top 6 inches of your tank, where the hottest water is located. There should be a discharge pipe that is directed into some sort of drain either in the floor or some other safe location where it will not come into contact with any people or animals…that water is hot!
Even when no problem has been identified with the water heater, the TPR should be proactively inspected every three years by a licensed plumber. It is difficult to diagnose problems with a TPR valve, so it’s best left to experts.
If you hear any water trickling or gushing out of your water heater on a regular basis, or it’s been more than three years since your water heater was inspected by a professional, it’s time to schedule a service call.