T&P Relief Valve Testing
Updated February 24, 2026
The T&P (temperature and pressure) relief valve is the single most important safety device on your water heater. If the temperature or pressure inside the tank exceeds safe limits, this valve opens and releases water to prevent the tank from becoming a bomb. That's not an exaggeration -- a water heater without a functioning T&P valve can explode with enough force to launch through a roof. Testing it takes 60 seconds.
Overview
The T&P (temperature and pressure) relief valve is the single most important safety device on your water heater. If the temperature or pressure inside the tank exceeds safe limits, this valve opens and releases water to prevent the tank from becoming a bomb. That's not an exaggeration -- a water heater without a functioning T&P valve can explode with enough force to launch through a roof. Testing it takes 60 seconds.
What to Know
How the T&P Valve Works
- The valve has a spring-loaded mechanism calibrated to open at 150 PSI or 210 degrees Fahrenheit -- whichever comes first.
- When triggered, it releases hot water through a discharge pipe that should run down to within 6 inches of the floor or to a drain.
- This drops the tank pressure and temperature to safe levels.
Where to Find It
- The T&P valve is on the side or top of the water heater tank.
- It has a lever or test handle on it and a discharge pipe (usually copper or CPVC) running down from it.
- The discharge pipe must not be capped, plugged, or reduced in size -- the water needs a clear path out.
What the Discharge Pipe Must Do
- The pipe must run downward to within 6 inches of the floor or to a drain.
- It cannot be threaded or connected to the drain system directly (air gap required).
- It cannot have any valves or restrictions on it.
- It should be the same diameter as the T&P valve outlet.
- If your discharge pipe doesn't meet these requirements, it's a safety hazard.
Safety Warnings
- Directing the discharge pipe upward or into a wall. Hot water must exit safely to a visible location.
Step by Step
- Place a bucket under the discharge pipe
The water that comes out will be hot. Place a bucket at the end of the discharge pipe to catch it. If the pipe runs to a floor drain, you can skip the bucket.
- Lift the test lever
Lift the lever on the T&P valve for about 5 seconds. Hot water should flow forcefully through the discharge pipe. You'll hear it rush out. This confirms the valve opens properly.
- Release the lever
Let the lever snap back to the closed position. The water flow should stop immediately. If it continues dripping, lift and release the lever once more to reseat the valve. A valve that keeps dripping after two or three attempts needs replacement.
- Check for leaks
After testing, watch the discharge pipe for 5 minutes. There should be no dripping. A slow drip means the valve isn't seating properly -- replace it. A valve that's never been tested on an old heater may not reseat well after the first test.
Pro Tips
- Test the T&P valve once a year as part of your water heater maintenance routine.
- If the valve has never been tested and the heater is more than 5 years old, be prepared for it to drip after testing. Have a replacement on hand.
- T&P valves cost $15-$30 and thread in and out without draining the tank. Replacement is a 15-minute job.
- Never plug, cap, or remove the T&P valve. Ever. For any reason.
Mistakes to Avoid
- Never testing the T&P valve -- a stuck valve can't protect you.
- Capping the discharge pipe because it dripped once. Replace the valve instead.
- Ignoring a T&P valve that discharges frequently. This means pressure or temperature in the tank is too high -- diagnose the cause (faulty PRV, no expansion tank, thermostat set too high).
- Directing the discharge pipe upward or into a wall. Hot water must exit safely to a visible location.
When to Call a Pro
If the T&P valve is discharging regularly during normal operation, a plumber needs to diagnose whether it's a thermal expansion issue, a failed PRV, or an overheating problem. If you can't replace the valve yourself (it requires a pipe wrench and working with hot water connections), a plumber can do it in 15 minutes.
Bottom Line
Lift the lever, water rushes out, release the lever, water stops. That's the test. Sixty seconds once a year confirms your water heater's primary safety device works. There is no maintenance task with a higher consequence-to-effort ratio.
Frequently Asked Questions
What are expert tips for t&p relief valve testing?
Test the T&P valve once a year as part of your water heater maintenance routine. If the valve has never been tested and the heater is more than 5 years old, be prepared for it to drip after testing. Have a replacement on hand. T&P valves cost $15-$30 and thread in and out without draining the tank. Replacement is a 15-minute job. Never plug, cap, or remove the T&P valve. Ever. For any reason.
What mistakes should I avoid with t&p relief valve testing?
Never testing the T&P valve -- a stuck valve can't protect you. Capping the discharge pipe because it dripped once. Replace the valve instead. Ignoring a T&P valve that discharges frequently. This means pressure or temperature in the tank is too high -- diagnose the cause (faulty PRV, no expansion tank, thermostat set too high). Directing the discharge pipe upward or into a wall. Hot water must exit safely to a visible location.
When should I call a professional for t&p relief valve testing?
If the T&P valve is discharging regularly during normal operation, a plumber needs to diagnose whether it's a thermal expansion issue, a failed PRV, or an overheating problem. If you can't replace the valve yourself (it requires a pipe wrench and working with hot water connections), a plumber can do it in 15 minutes.
What is the bottom line on t&p relief valve testing?
Lift the lever, water rushes out, release the lever, water stops. That's the test. Sixty seconds once a year confirms your water heater's primary safety device works. There is no maintenance task with a higher consequence-to-effort ratio.
When should I call a professional for t&p relief valve testing?
If the T&P valve is discharging regularly during normal operation, a plumber needs to diagnose whether it's a thermal expansion issue, a failed PRV, or an overheating problem. If you can't replace the valve yourself (it requires a pipe wrench and working with hot water connections), a plumber can do it in 15 minutes.
What's the bottom line on t&p relief valve testing?
Lift the lever, water rushes out, release the lever, water stops. That's the test. Sixty seconds once a year confirms your water heater's primary safety device works. There is no maintenance task with a higher consequence-to-effort ratio.
How much does t&p relief valve testing cost?
The typical cost range is $0 for testing / $15-$30 for replacement. Actual costs depend on your location, materials, and whether you hire a professional.
How difficult is t&p relief valve testing?
This task is rated Easy. It requires moderate DIY skill.