The temperature and pressure relief valve — the T&P valve — is the single most important safety device on your water heater. It's designed to open and release water if the temperature or pressure inside the tank climbs to a dangerous level, preventing the tank from bursting. If your T&P valve leaks constantly, is corroded, or fails a test, it should be replaced right away. Fortunately, it's an inexpensive part and a manageable DIY job.
How to Tell If the Valve Needs Replacing
Test the valve by placing a bucket under the discharge pipe and gently lifting the lever for a few seconds. Water should flow while the lever is up and stop cleanly when you release it. Replace the valve if: it keeps dribbling after you release the lever, it doesn't release any water at all when lifted, or you see rust and corrosion on the valve body. A valve that discharges frequently on its own can also indicate a pressure problem worth investigating.
What You'll Need
Gather a new T&P valve rated for your heater, a pipe wrench, Teflon (thread-seal) tape, a bucket, and a garden hose. Buy the correct valve — match the temperature and pressure rating (commonly 150 psi / 210°F) and the thread size for your tank.
Step 1: Turn Off Power and Water
For a gas heater, set the gas control to "Pilot" or off; for electric, switch off the breaker. Then close the cold water supply valve at the top of the tank so no more water enters.
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Step 2: Relieve Pressure and Drain a Little
Open a hot water faucet in the house to relieve pressure. Connect a garden hose to the drain valve and drain a few gallons — enough to lower the water level below the T&P valve, which is usually mounted on the top or upper side of the tank. This prevents a gush of water when you remove the old valve.
Step 3: Remove the Discharge Pipe and Old Valve
Unscrew the discharge pipe (the tube running down from the valve toward the floor). Then use a pipe wrench to unscrew the old T&P valve counter-clockwise. Some water will trickle out — that's normal.
Step 4: Install the New Valve
Wrap the threads of the new valve with Teflon tape, three or four turns in a clockwise direction, for a leak-proof seal. Thread the new valve in by hand first to avoid cross-threading, then tighten it snugly with the wrench so the valve is oriented correctly and the discharge port points down. Reattach the discharge pipe, making sure it points toward the floor and stops a few inches above it — never cap or thread the end.
Step 5: Refill and Test
Close the hot faucet, turn the cold water supply back on, and let the tank refill. Check the new valve and connections for leaks. Restore power or gas, let the water heat, and test the new valve once by lifting the lever briefly and confirming it seals when released.
Conclusion
Replacing a T&P valve is a straightforward repair that protects your home from a dangerous over-pressure situation. Always work with the power and water off, drain below the valve first, seal the threads properly, and keep the discharge pipe pointed at the floor. If the valve keeps discharging after replacement, you may have an excess-pressure issue — call a professional to investigate.