Temperature and Pressure Relief Valve for Water Heating

How and when to replace a Temperature and Pressure Relief Valve in water heaters. Find out how T&P valve, as the safety component, brings you reliable water heating and what you should do to keep it operational.

What is a Temperature and Pressure Relief Valve

Temperature and Pressure Relief Valve or short T&P is the safety device that is found on all types of water heaters, and is designed to prevent water from boiling or overheating. If T&P is not installed, there will be a lot of stress on water heater caused by the extreme pressure and temperature, which might cause the deformation and rupture of the unit.

Note: Every water tank heater has the Temperature and Pressure Relief Valve factory installed, while on tankless appliances, PRV or pressure relief valve is recommended.

T&P is mainly installed on a side of the heater (the upper part), but can be located at the top of the unit also. It should be immersed in the top six inches of the heater, where water is the hottest.

How it works

As said, TPR valve is factory installed on all water tank heaters, designed for pressures up to the maximum of 150 PSI in residential applications. T&P is also designed to open when the pressure inside the tank exceeds this value or if the temperature exceeds values close to the boiling
(212 F).

Also, it is recommended to install a discharge pipe on every TPR valve, which will direct the excessive vapor or hot water downward to the floor drain and terminate at least 6" above. Keep in mind that any discharge means the unsafe condition inside the water heater, so you should always contact the technician.

emergency plumber

Problems and how to avoid them

The most dangerous situation is if the TPR valve doesn't work and there is an excessive pressure and temperature buildup inside the water heater.

The most frequent problem is related to the hard water and mineral deposits in the valve seat, which prevents it from closing tightly. Also, due to the thermal expansion in the closed water systems, you might see that the valve discharges or makes the popping noise periodically.

Testing the TPR valve

This is why you should test the relief valve regularly. Test the element by lifting and releasing the lever slowly and see does it opens and closes freely. Allow several gallons of water to flush through the discharge line. If the relief valve fails to close, and still releasing the water, shut the unit off and call a plumber or replace the element.

T&P should never be altered or repaired, always install a new one, which must be per code and with the sufficient rating (manufacturer recommended). There should be no obstruction between the TPR and the tank.

How to replace a Temperature and Pressure Relief Valve

  • Turn the power off (electricity and gas supply if applicable).

  • Attached one end of the garden hose to the drain valve and terminate the other end outside or to the floor drain.

  • Close the water supply on the shut off spigot.

  • Open T&P, then open the drain spigot. Be careful as water might be hot.

  • Close the drain spigot when the water stops running.

  • Remove the old T&P valve.

  • Use a pipe sealer or Teflon type on the threads and install the new valve. T&P valve should be in the open position.

  • Open the hot water tap and shut off valve on the cold water line.

  • Close the relief valve once the water starts flowing in the steady stream.

  • Turn the hot water tap off once the steady stream of water is established.

  • Make sure the tank is full before running the heater. Turn the power on.

  • Test the Temperature and Pressure Relief Valve once again.

As said before, Temperature and Pressure Relief Valve is the safety element that must work properly anytime, while rated equal or higher than the working pressure (found on the rating plate), protected from freezing and without any obstructions, including the discharge pipe.

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