How to Replace a Water Heater's T&P Relief Valve

For an electric water heater, locate the corresponding double-pole circuit breaker in your home's main electrical panel and switch it to the 'OFF' position. For a gas heater, find the gas shutoff valve on the supply line leading to the heater's gas control valve and turn it to the 'OFF' position (the handle should be perpendicular to the pipe). Next, locate the cold water inlet pipe at the top of the water heater and turn its shutoff valve clockwise until it stops. This isolates the heater from power and water, ensuring a safe working environment.

Attach a standard garden hose to the drain valve located near the bottom of the water heater tank. Route the other end of the hose to a floor drain, utility sink, or outside, ensuring the exit point is lower than the drain valve itself. To allow air into the tank and prevent a vacuum, open a hot water faucet at a sink somewhere in your house. Then, fully open the drain valve on the water heater (this may require a flathead screwdriver or a handle). You only need to drain enough water so the level is below the T&P valve you are replacing, not the entire tank.

The T&P valve has a discharge pipe, typically made of copper or CPVC, that directs water towards the floor. Using a pipe wrench or a large adjustable wrench, grip the fitting that connects this pipe to the T&P valve's outlet and turn it counter-clockwise to loosen and remove it. Be prepared for a small amount of trapped water to spill out; having a small bucket and rag handy is useful.

Place a large pipe wrench over the hexagonal body of the old T&P valve itself. Position the wrench so you can apply force in a counter-clockwise direction. This may require significant leverage, as the valve is often sealed tightly. Pull firmly on the wrench to break the seal and unscrew the valve completely from the water heater tank. Keep a bucket underneath to catch any remaining water that spills from the opening.

Use a clean rag to wipe the female threads on the water heater tank, removing any old sealant or debris. Take your new T&P relief valve and wrap the male threads with 3 to 4 layers of Teflon tape. It is crucial to wrap the tape in a clockwise direction (the same direction you will tighten the valve). This prevents the tape from unravelling during installation. Carefully thread the new valve into the tank opening by hand to avoid cross-threading. Once it's hand-tight, use the pipe wrench to tighten it another 1-2 full turns, until it is snug and the outlet is pointing downwards. Do not overtighten.

Thread the discharge pipe back onto the outlet of the newly installed T&P valve. If the connection requires it, apply new Teflon tape to the male threads of the pipe. Tighten the connection using your pipe wrench or adjustable wrench until it is secure. Per plumbing codes, the pipe must be made of an approved material (like copper or CPVC), be the same diameter as the valve outlet, and terminate within 6 inches of the floor or an approved indirect receptor. The end of the pipe must not be capped or threaded.

Ensure the water heater's drain valve is fully closed. Double-check that the hot water faucet you opened earlier is still open. Go to the cold water inlet valve and slowly turn it counter-clockwise to open it. You will hear water begin to fill the tank. Keep the hot water faucet open until you have a steady, air-free stream of water coming out. This indicates the tank is full and all air has been purged. Once full, close the hot water faucet. Thoroughly inspect the new T&P valve and the discharge pipe connection for any drips or leaks.

Once you have confirmed that there are no leaks and the tank is full, go to the electrical panel and switch the water heater's circuit breaker back to the 'ON' position. For a gas heater, follow the manufacturer's instructions to relight the pilot light. Allow the heater 30-60 minutes to heat the water. As a final check, place a bucket under the discharge pipe and briefly lift the test lever on the T&P valve. A burst of hot water should discharge, and the valve should snap shut cleanly when you release it. This confirms it is functioning correctly.