How to Check a Water Heater T&P Valve
Updated February 25, 2026
Test the temperature and pressure relief valve on your water heater to make sure it works -- the safety device that prevents tank explosions.
Overview
The T&P (temperature and pressure) relief valve is the most important safety device on your water heater. If the thermostat fails and the water overheats, or if pressure builds beyond safe limits, the T&P valve opens and releases water to prevent the tank from rupturing. A ruptured water heater is not a leak -- it is an explosion that can launch a 40-gallon tank through a roof. Testing the T&P valve takes 30 seconds and should be done annually. If it does not work, replace it immediately -- $15-$25 part, 15-minute job.
What You'll Need
Safety First
- The water that discharges from the T&P valve is 120-140°F. Keep hands, feet, and children away from the discharge pipe when testing.
- The discharge pipe should route to within 6 inches of the floor or to an exterior drain. Never cap, plug, or remove the discharge pipe -- that defeats the safety function.
- If the T&P valve is leaking continuously (not just during testing), do not ignore it. Either the valve is faulty or the tank pressure/temperature is too high. Both need immediate attention.
Step-by-Step Instructions
- Locate the T&P Valve
The T&P valve is on the side of the tank near the top, or on top of the tank. It has a metal lever (flip-up handle) and a discharge pipe running downward from it. The discharge pipe should terminate 6 inches above the floor or route to a floor drain. If there is no discharge pipe, that is a code violation -- add one before testing, or water will spray sideways when you lift the lever.
Tip: Some T&P valves are on top of the tank and the discharge pipe runs down the side. Others are on the side near the top with a short discharge pipe pointing down. Either location is correct. - Test the Valve
Place a bucket under the end of the discharge pipe. Lift the metal lever on the T&P valve straight up. You should hear a rush of air and/or see hot water discharge from the pipe. This means the valve opened -- it is working. Release the lever. The valve should snap shut and the discharge should stop completely. No water, no drip.
Tip: Lift the lever briskly and hold it for 3-5 seconds. A hesitant, slow lift sometimes does not open the valve fully. If nothing happens on a brisk lift, the valve is stuck and needs replacement. - Evaluate the Results
Three possible outcomes. Good: water discharged when you lifted the lever and stopped completely when you released it. The valve works. Replace: no water discharged when you lifted the lever, or the lever would not move at all. The valve is stuck or seized -- replace it immediately. Concerning: water discharged but continues to drip after you release the lever. The valve seat is fouled with mineral deposits and is not sealing. Replace it.
Tip: A T&P valve that drips after testing sometimes reseats itself after a few minutes. Wait 10 minutes. Still dripping? Replace it. Mineral deposits on the seat prevent a clean seal. - Replace If Needed
Turn off the heat source. Turn off the cold water inlet. Drain the tank a few inches below the T&P valve location. Unscrew the discharge pipe from the valve. Unscrew the valve from the tank with a pipe wrench (turn counterclockwise). Wrap the new valve threads with Teflon tape (4-6 wraps). Thread the new valve in and tighten. Reconnect the discharge pipe. Refill the tank, restore heat, and test the new valve.
Tip: T&P valves are rated by pressure (150 PSI is standard residential) and temperature (210°F). Match the rating of the old valve. The rating is stamped on the valve body. Watts 100XL ($15-$20) is the most common residential replacement.
Pro Tips
- Test the T&P valve annually. It is a 30-second task that verifies the most critical safety device on the water heater. Put it on the same calendar reminder as smoke detector battery checks.
- T&P valves have a lifespan of 5-7 years. If yours is original and the heater is 5+ years old, replace it proactively. A $15 valve is cheap compared to the consequences of a non-functional one.
- A T&P valve that opens on its own (without you testing it) is responding to excess pressure or temperature. Check: is the thermostat set too high? Is there a thermal expansion issue (no expansion tank on a closed system)? Is the water pressure above 80 PSI? Fix the root cause, then replace the valve.
- The discharge pipe must not be reduced in size (same diameter as the valve outlet), must not be capped or plugged, must not route uphill, and must terminate where discharged water is visible. These are code requirements, not suggestions.
- Never use a T&P valve as a regular pressure relief device. If it opens frequently, install an expansion tank ($40-$100) to absorb thermal expansion. The T&P valve is for emergencies only.
When to Call a Pro
Call a plumber if the T&P valve opens repeatedly on its own (indicates a pressure or temperature problem that needs diagnosis), if there is no discharge pipe and you need one installed to code, if the valve is corroded into the tank and will not unscrew (risk of damaging the tank threads), or if you are unsure whether the valve is working correctly.
Frequently Asked Questions
When should I call a plumber to check a water heater t&p valve?
Call a plumber if the T&P valve opens repeatedly on its own (indicates a pressure or temperature problem that needs diagnosis), if there is no discharge pipe and you need one installed to code, if the valve is corroded into the tank and will not unscrew (risk of damaging the tank threads), or if you are unsure whether the valve is working correctly.
What are some expert tips to check a water heater t&p valve?
Test the T&P valve annually. It is a 30-second task that verifies the most critical safety device on the water heater. Put it on the same calendar reminder as smoke detector battery checks. T&P valves have a lifespan of 5-7 years. If yours is original and the heater is 5+ years old, replace it proactively. A $15 valve is cheap compared to the consequences of a non-functional one. A T&P valve that opens on its own (without you testing it) is responding to excess pressure or temperature. Check: is the thermostat set too high? Is there a thermal expansion issue (no expansion tank on a closed system)? Is the water pressure above 80 PSI? Fix the root cause, then replace the valve. The discharge pipe must not be reduced in size (same diameter as the valve outlet), must not be capped or plugged, must not route uphill, and must terminate where discharged water is visible. These are code requirements, not suggestions. Never use a T&P valve as a regular pressure relief device. If it opens frequently, install an expansion tank ($40-$100) to absorb thermal expansion. The T&P valve is for emergencies only.
What tools do I need to check a water heater t&p valve?
You will need: Bucket (to catch discharge water during testing), Pipe wrench (for valve replacement if needed), Replacement T&P valve ($15-$25, Watts 100XL or equivalent), Teflon tape (for thread sealing on replacement).
When should I call a professional instead of doing this myself?
Call a plumber if the T&P valve opens repeatedly on its own (indicates a pressure or temperature problem that needs diagnosis), if there is no discharge pipe and you need one installed to code, if the valve is corroded into the tank and will not unscrew (risk of damaging the tank threads), or if you are unsure whether the valve is working correctly.
How difficult is this project?
This project is rated easy. Most homeowners with basic tools can complete it.
How long does this take?
Plan for approximately 5 - 10 minutes. First-timers may need extra time.
How much will this cost?
The estimated cost is $0 (testing); $15 - $25 for replacement. Costs vary by location and materials chosen.