Water Heater Pressure Relief Valve: Dripping, Testing, and Replacing

The temperature and pressure relief valve (usually called the T&P valve or TPR valve) is a small brass fitting on the side of your water heater with a lever on top and a pipe running down toward the floor. Most homeowners never think about it until it starts dripping. But this valve is the single most important safety device on your water heater, and ignoring a problem with it can have real consequences.

This guide covers what the T&P valve actually does, why it drips, how to test it, when to replace it, and how to do the replacement yourself if you're comfortable with basic plumbing.

What the T&P Valve Does

Water heaters are sealed pressure vessels. When a thermostat fails or a cold-water supply valve is accidentally closed, temperature and pressure inside the tank can climb to dangerous levels. Without a relief valve, a tank under extreme pressure can rupture or, in rare cases, rocket through walls and ceilings like a missile.

The T&P valve prevents this. It opens automatically if the water temperature exceeds 210°F or the pressure exceeds 150 psi. When either threshold is reached, the valve releases water through a discharge pipe until conditions return to safe levels, then closes again.

Most homeowners will never see their T&P valve open during normal operation. It's a last line of defense, not something that should be opening on a regular basis.

Why Your T&P Valve Is Dripping

A dripping or weeping T&P valve is the most common complaint, and it almost always means one of three things:

1. The valve is doing its job

If your water heater is set too high, or if your home has high water pressure, the T&P valve may be opening briefly as it's designed to. A setting above 120–125°F or household water pressure above 80 psi can be enough to cause periodic dripping. Check your temperature setting (the dial on the thermostat) and consider installing a pressure-reducing valve if your supply pressure is running high.

2. Thermal expansion

If your home has a "closed" plumbing system (where a backflow preventer or check valve stops heated water from expanding back into the supply line), pressure inside the tank builds every time the water heats up. This is one of the most common causes of a dripping T&P valve and the reason most plumbing codes now require an expansion tank on closed systems.

3. The valve has failed and needs replacement

T&P valves contain a spring and seat that wear out over time. A valve that has been partially opened, even once during a test, can develop a slow drip if mineral deposits prevent the seat from fully closing. A valve that drips continuously, that won't stop after you reduce temperature and pressure, or that is more than 5 years old should simply be replaced.

Is a Dripping T&P Valve Dangerous?

A dripping valve on its own isn't an emergency, but it tells you something is wrong and shouldn't be ignored for long. The real danger comes from two failure modes at opposite ends:

A valve that won't close: Continuous discharge means you're losing hot water and possibly damaging floors and walls. A valve stuck open also can't protect the tank if a real overpressure event occurs.
A valve that's been capped or disabled: Some homeowners (or previous owners) cap the discharge pipe or wedge the lever to stop a persistent drip. This is extremely dangerous. A capped T&P valve cannot release pressure. Never cap, plug, or disable a T&P valve for any reason.

How to Test Your T&P Valve

Most manufacturers and plumbing codes recommend testing the T&P valve once a year. The test is quick, but you're dealing with scalding water, so a few precautions first:

Make sure the discharge pipe points down toward the floor or a drain, not toward you
Don't stand directly in front of or under the discharge pipe during the test
Have a bucket ready if there's no floor drain nearby

Locate the lever on the T&P valve. It should be on the side of the tank, roughly in the upper third, with a metal discharge pipe running down from it.
Lift the lever briefly (about one second), then let it snap back down.
Hot water should discharge from the pipe while you hold the lever up. When you release it, the flow should stop completely within a few seconds.
If no water flows when you lift the lever, the valve may be seized and should be replaced.
If water continues dripping after you release the lever, the valve seat is compromised. Replace the valve.

One important caution: On older water heaters, lifting the lever on a valve that hasn't been tested in years can cause it to start dripping and never fully stop. Once you disturb it, the mineral buildup that was keeping the seat sealed is gone. If your heater is over 10 years old and the valve has never been tested, it's often better to replace it proactively rather than risk triggering a drip you can't stop.

Not sure how old your water heater is? Use our free age-check tool to decode the serial number and find out.

When to Replace the T&P Valve

Replace your T&P valve if any of the following are true:

It drips or weeps and the problem isn't resolved by reducing temperature or pressure
It continues dripping after a lift test
It fails to discharge water during a test (likely seized)
It shows visible corrosion, rust, or mineral buildup on the body
It is more than 5–6 years old. Most manufacturers recommend replacement on this schedule even without symptoms.
Your water heater is approaching or past 10 years old. A T&P valve replacement is cheap insurance before other things start failing.

How to Replace a T&P Valve Yourself

This is a manageable job for anyone comfortable shutting off water supply lines and working around a hot water tank. Budget about 30–60 minutes. The valve itself costs $15–$40.

What you'll need

A replacement T&P valve rated for your heater's BTU or wattage and pressure (check the label on your existing valve and match the BTU rating exactly)
Pipe wrench or large adjustable wrench
Teflon tape (PTFE thread tape)
A bucket

Steps

Turn off the heater. For gas heaters, turn the thermostat to "Pilot." For electric heaters, flip the breaker at the panel.
Turn off the cold-water supply. There's a shutoff valve on the cold inlet line above the heater.
Drain a few gallons from the tank. Connect a hose to the drain valve at the bottom of the tank and open it briefly, or open a hot-water tap in the house to reduce pressure. You don't need to drain the whole tank.
Disconnect the discharge pipe. The pipe attached to the T&P valve outlet is usually threaded or connected with a union. Unscrew or disconnect it and set it aside.
Unscrew the old T&P valve. Use a pipe wrench on the valve body (not the lever) and turn counterclockwise. It may take some force if it's been in place for years.
Wrap the threads of the new valve. Apply two or three wraps of Teflon tape clockwise around the threads of the new valve's inlet.
Install the new valve. Thread it in by hand first, then tighten with the pipe wrench. The outlet (where the discharge pipe attaches) should point down or to the side, never straight up.
Reattach the discharge pipe. Make sure it points down toward the floor and terminates within 6 inches of the floor or over a drain.
Restore water supply and power. Open the cold-water shutoff, let the tank refill (you'll hear it filling), then restore power or relight the pilot.
Check for leaks. Inspect the valve body and threads for any drips after the tank is up to pressure.

If any of these steps feel out of your comfort zone, particularly shutting off gas or working around the discharge piping, call a licensed plumber. The job typically runs $75–$150 in labor.

The Discharge Pipe: What It Must and Must Not Do

The discharge pipe attached to your T&P valve is just as important as the valve itself. Plumbing codes are specific about it for good reason:

Must: Be the same diameter as the valve outlet (usually ¾ inch), run continuously downward, and terminate within 6 inches of the floor or over a floor drain
Must: Be made of a material rated for 210°F: copper, CPVC, or steel. Plain PVC can soften under a hot discharge and should not be used.
Must not: Be capped, plugged, or reduced in diameter at any point
Must not: Discharge directly onto the water heater, electrical components, or in a way that creates a scalding hazard

If your discharge pipe is missing, made of plain PVC, reduced in size, or terminates somewhere other than near the floor, have it corrected when you replace the valve.

Frequently Asked Questions

How much does it cost to replace a T&P valve?

The valve itself costs $15–$40 at any hardware store. If you hire a plumber, expect to pay $75–$200 total including labor. The job usually takes less than an hour.

Can I replace the T&P valve myself?

Yes, if you're comfortable shutting off water lines and working around a water heater. The main thing to get right is matching the new valve's BTU or wattage rating to the old one. Always match the rating stamped on the old valve exactly.

My T&P valve is dripping but the heater is not that old. Is this normal?

Not exactly normal, but common. The most likely causes are high water pressure (above 80 psi), thermal expansion in a closed plumbing system, or a temperature setting above 125°F. Check your water pressure with an inexpensive gauge (available at any hardware store) and consider adding an expansion tank if you have a closed system.

What happens if I ignore a dripping T&P valve?

A continuously dripping valve will eventually fail to close fully, which means it can no longer protect the tank in an overpressure event. It can also cause water damage near the discharge pipe. Don't put it off. A new valve costs under $40 and the swap takes less than an hour.

Is it safe to cap the discharge pipe to stop the drip?

No. Never cap, plug, or crimp the discharge pipe or wedge the lever open or closed. A disabled T&P valve is a serious safety hazard. Fix the underlying cause or replace the valve.

How often should I test my T&P valve?

Once a year is the standard recommendation. If your heater is over 10 years old and the valve has never been tested, consider replacing it proactively rather than testing it. A seized valve that has been held shut by mineral buildup can start dripping once the lever is lifted and never fully close again.