Repairing the Temperature & Pressure Relief Valve

The temperature and pressure (T & P) relief valve is the most important safety component on a water heater. It prevents excessive pressure from building up inside the tank and causing an explosion. If the temperature of the water inside the tank exceeds approximately 200 degrees Fahrenheit, because a malfunctioning thermostat and a high-limit switch allows the heating source to remain on, the T & P relief valve opens to allow hot water or steam to pour out the relief tube. Pressure inside the tank is reduced to a safe level.

This section describes how to know when the valve has malfunctioned and how to install a new valve. The valve is located on the side or on the top of the tank.

Signs of trouble
Water dripping from the pipe connected to the T & P relief valve is a sign that the valve is weak and should be replaced. Make sure the water temperature is not too hot - creating extra pressure - because of an improperly set thermostat.

Test the operation of a T & P relief valve every so often to make sure the valve is still operative. Place a pail under the T & P relief pipe and lift the lever of the valve (Fig. 1). Water should flow out of the pipe, and it should stop when the valve is released. If not, replace the valve.

Replacing a T&P relief valve
Here's how to proceed:

1) Buy a replacement valve
Buy a new T & P relief valve from a plumbing-supply store or home center. The valve to get is one that has the same Btu/h (British thermal unit per hour) rating as the water heater. Check the data plate attached to the water heater to find out what this rating is.

2) Shut off gas/electricity and water
With the gas or electricity to the unit turned off, close the shutoff valve of the cold-water pipe. Do not use any faucets in the house. If this is not possible, turn off the main water supply.

3) Drain the water
Put on safety goggles. Open the relief valve, and drain the water to the elevation of the valve.

4) Remove relief pipe
Using a pipe wrench to hold the T & P relief valve, turn the relief pipe out of the valve with another pipe wrench.