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How To Test And Replace Your Water Heater's Relief Valve - Plumb University

How To Test And Replace Your Water Heater’s Relief Valve

by Trevor Woods | Last Updated: May 13, 2020

Want to know a secret? You have a potential bomb in your basement, a missile in your mechanical room, a plumbing projectile, you get the idea. The most important safety device in your home is found on your water heater.

On the very top or on the side of your hot water tank is a brass valve called a Temperature and Pressure Relief Valve, or T&P valve for short. This T&P valve is an emergency safety device that prevents or relieves excessive temperature or pressure. And without a Temperature And Pressure Relief Valve, your heater could rupture or explode damaging property and potentially harming you or your family.

The power of pressure buildup in your water heater can be powerful enough to propel your hot water tank through your home soaring into the sky. Check out this footage from an episode of MythBusters.

Although rare, the danger is very real. In a perfect world, you will never need to use your hater heater’s T&P valve but it’s critical that you know how your hot water tank’s safety features work, how to maintain and test them, and replace them when necessary to protect your home.

How Do T&P Valves Work?

The Temperature and Pressure Relief Valve is a 2-in-1 one device that reacts to unsafe temperatures and pressures. Most residential water heaters have T&P valves rated for 210° F and 150 psi.

Your water heater’s relief valve is located in the top six inches of your hot water tank. Whether the T&P valve is located on the very top or on the side, it’s temperature probe will be submersed in the hottest water inside the tank.

If the temperature probe of the T&P relief valve senses water temperatures of 210° F, it will be triggered to open to prevent the water from boiling. When the relief valve opens it will discharge the hot water at the top of the tank and allow cold water from the inlet to enter the water heater to reduce the water temperature inside the tank.

The temperature relief valve will continue to stay open and expel water until the probe cools and closes the discharge outlet. When this happens you will see a large volume of water that will be discharged before the unsafe condition is over.

The other half of the water heater safety equation is pressure. Your home’s hot water system is essentially a closed-loop. And when water is heated, it expands. The volume of water can increase upwards of 4% as it reaches its boiling point. That means a 40-gallon hot water tank can increase its volume by 1.6 gallons with nowhere for this water to flow.

Water heaters are designed to handle some thermal expansion but too much pressure will actuate the pressure relief valve. Most hot water tanks have T&P valves rated for 150 psi and any buildup over that limit and you will see the valve dribble and weep on the floor from the discharge tube until the internal pressure drops below 150 psi.

During the normal operation of your water heater the T&P relief valve remains closed but it stands as the last line of defense for pressurized vessels and catastrophic failure. If the water inside your hot water tank was pressurized and superheated, the water could flash to steam with the explosive potential of over two million foot-pounds of energy! That’s why relief valves come standard on water heaters and are mandated by plumbing codes for hydronic systems.

Temperature And Pressure Relief Valve

This Temperature and Pressure Valve will help protect your home's water heater from excessive temperature and water pressure.

It features an epoxy-coated probe to prevent corrosion buildup.

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Why Do T&P Valves Fail?

Temperature and mineral deposits are the two most common causes to have problems with your water heater relief valve. If your T&P valve constantly dribbles or is weeping, this can cause mineral deposits to build up on the valve seat. This foreign material on the valve seat will prevent it from sealing properly and closing water-tight.

Because the T&P valve sits in the hottest portion of water inside the tank it is constantly exposed to high temperatures. Heat and mineral deposits can cause the valve to stiffen over time. This results in a sticky valve that can prevent it from opening or closing properly.

How To Test Your Relief Valve

Typically, your T&P valve will last as long as your water heater and most manufacturers recommend testing your relief valve once a year. This will make sure that the T&P will function properly in case of an emergency and catch any problems early. Naturally occurring conditions can corrode the valve or its components over time. If the valve fails to test properly, it must be replaced.

1. Inspect The Discharge Tube

Before you test the relief valve itself, check the discharge tubing to make sure it is firmly connected to the T&P valve. There should be no valves installed on this piping and it should not be capped or plugged in any way. In order to avoid accidental scalding to water damage, the discharge line should run or drain to a safe location like a floor drain.

2. Pull The Test Lever

Now is the time to test the relief valve itself. If the T&P valve is not piped to a floor drain, place a bucket below the discharge tube. Lift the small metal handle to cause a small amount of water to release from the valve and release the handle and let it snap back into its original position.

Protect Your Toes

Wear closed-toe shoes and pants while testing relief valves to prevent accidental scalding.

3. Check For Leaks

If no water flows from the valve or the T&P fails to close completely after testing the valve must be replaced. If the relief valve continues to leak after testing there is the possibility that some debris or water deposits are preventing the valve from closing completely.

You can try opening and closing the T&P valve a few times to try and flush any obstructions out of the valve but if it continues to leak the relief valve will need to be replaced.

How To Troubleshoot A Leaky T&P Valve

The first thing you want to do when looking to repair a water heater’s relief valve is to confirm that a safety issue isn’t present. Check the water temp and see if it is set too high. We recommend setting the temperature of your hot water tank to 120° F.

Also, take a look at your water pressure to ensure that your system isn’t overpressurized. Water pressure over 80 PSI is considered excessive and a Pressure Reducing Valve (PRV) should be installed.

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Now that you have ruled out any hazardous water scenarios let’s take a serious look at resolving your T&P valve issues. Unfortunately, many homeowners mistake a leaky relief valve discharging water on the floor as water heater failure. However, there are some general guidelines that will help you diagnose your T&P relief valve.

Watch Out For Water Damage

The discharge from a T&P valve as well as the brass valve body itself can be very hot! Make sure you avoid contact with your skin and take preventative measures for any water spilling from your relief valve discharge tube. Prevent water damage to your home by ensuring that the T&P discharge is piped to a floor drain or collected safely to be disposed of later.

Dribbling Or Weeping Relief Valve

If you notice a small amount of water seeping out from your T&P valve and collecting on the floor, this is most likely the result of over-pressurization. If your home has a Pressure Reducing Valve (PRV) or backflow prevention device installed on your water main, this may be causing your T&P valve to drip occasionally.

These PRV or backflow valves create a closed water heating system in your home. Some water softeners or filtration systems may also have check valves built into them to prevent the reversed flow of water. This closed system will not allow for the thermal expansion of water in your hot water tank and will cause you T&P to drip occasionally.

To address this issue you will need to compensate for the thermal expansion of water with an expansion tank. Expansion tanks act as a buffer and absorb extra system pressure and protect your water heater from overpressurization. They will also protect your safety valve from failing or wearing out too quickly as well as extend the life of your hot water tank.

If you have a closed water heating system, installing an expansion tank on the cold inlet water line to your tank should remedy your leaking T&P valve from the water heater building too much pressure.

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Discharging Lots Of Water

If your relief valve is discharging large quantities of water, your hot water system is most likely running too high in temperature. The water heater is expelling a large volume of water to allow more cold water to enter the tank and cool the temperature inside.

You need to inspect your water heater’s temperature settings and check for failing thermostats on electric water heaters and control valves for gas water heaters.

Sticky Relief Valve Handle

A sticky relief valve can be the cause of a few serious problems. If a T&P valve is stuck in the downward or closed position it will be unable to prevent the overpressurization of the tank and the water heater may rupture. A relief valve that is stuck open will allow water to continually flow out of the discharge tube and potentially flood your home.

A finicky relief valve can sometimes be fixed by opening and closing the lever several times. This will “exercise” the valve and allow any debris that is caught in the valve seat to be flushed out. Jiggle the T&P valve by gently pulling the lever out towards yourself. Be careful of the discharge from the valve as it will be piping hot if the water heater is running.

If after a few attempts this technique doesn’t unstick the valve, then it is time to replace the relief valve.

How To Replace A T&P Valve

Replacing a worn-out or leaky relief valve is easy to do yourself in just a few minutes. When you replace your T&P valve, make sure that you are installing a relief valve that has the same BTU rating as the old one. These ratings are marked underneath the relief valve handle for quick reference.

Temperature And Pressure Relief Valve

This Temperature and Pressure Valve will help protect your home's water heater from excessive temperature and water pressure.

It features an epoxy-coated probe to prevent corrosion buildup.

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12/18/2023 05:35 am GMT

We recommend that you take this time to also install a water heater pan below the water heater to collect any slow drips or catch any emergency outflows of water in the future.

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Tools And Materials Needed

For real stubborn and tight relief valves we recommend using a T&P valve tool and a 7/8″ socket and breaker bar.

Temperature And Pressure Valve Remover

Remove and replace temperature and pressure valves safely and quickly.

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1. Turn Off Your Water Heater

Start off by turning off the water heater. This can be done at the circuit breaker for electric water heaters or the main control valve on gas powered models.

2. Drain The Water Heater

Attach a length of garden hose to the drain valve at the bottom of the water heater and run the other end of the hose to the nearest floor drain or a safe location for the water to drain.

Close the shutoff valve at the cold water inlet line to the hot water tank. Next, open a faucet somewhere in your home to relieve the system pressure inside the tank and allow it to drain properly.

Now, open the drain valve with a flat blade screwdriver and allow approximately 1 gallon of water to drain for a top-mounted T&P valve or 10 gallons for a side-mounted relief valve. Close the drain valve when you have released enough water so that it won’t spill out of the T&P valve when you remove it.

Hot Water Warning

Remember that the water will be hot so be careful not to scald yourself or others near the drain hose.

3. Remove The Old T&P Valve

Once the water level has drained below the level of the T&P valve, start by unthreading the discharge tube attached to the relief valve with an adjustable wrench or pipe wrench.

Now that the discharge piping is out of the way you can remove the old relief valve by turning it counterclockwise with a wrench.

Boost Your Torque

You may need to a use a cheater bar or snipe for extra leverage to break loose stubborn valves.

You may get some extra water leaking out of the T&P mounting location so have some rags or towels hand to soak up any spillage.

4. Install The New Relief Valve

Before you install the replacement valve, prepare the fitting threads with several wraps of Teflon Tape or Pipe-joint Compound.

Wrap Like A Pro

If you are using Teflon Tape, wrap the threads with tape in the same direction as you are going to install the fitting. In this case, apply the Teflon tape in a clockwise direction. This will prevent the tape from unravelling when you are screwing in the new T&P valve.

Make sure the new T&P and valve is in the closed position and begin screwing it clockwise into the mounting location with your hands. Be careful not to cross-thread the new relief valve in the tappings in the hot water tank.

Tighten up the T&P valve firmly with a wrench and try to finish installing the new valve so it ends up pointing in the same location as the old relief valve did.

Reconnect the T&P discharge tube to the valve and snug up this connection with a wrench. Make sure that the discharge piping points in a safe direction or drains to a floor drain or outside for safe disposal of hot water. The end of the discharge tube should terminate within 6 inches of the floor and not have any shut-off valve, plug, or cap installed on this discharge line.

Protect Your Plastic Pipes

If your discharge tubing is made of CPVC or plastic be careful not to over-tighten it. You could break the threads of the discharge tube off inside the T&P valve. A 1/4 turn with a wrench after it is hand tight is more than enough.

Relief Valve Runoff Tube

The runoff tube carries water steams safely to the drain pan or drain if the T&P valve activates.

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5. Fill Up The Water Heater

Keep the faucet you opened previously turned on and open the shut-off on the cold water inlet line to the hot water tank. You should hear the water heater starts to fill with water. You can open the lever on the T&P valve if you want to make it quicker for air to escape as the tank refills.

Once the water starts to flow steadily from the relief valve or the opened faucet, turn both locations off.

Check the relief valve for any leaks around the threads and tighten more if necessary.

6. Turn Your Water Heater Back On

Finish off by turning your water heater back on. Electric tanks can be switched on at the circuit breaker and gas water heaters at the main control valve.

You may need to relight the pilot on your water heater. Follow the instructions printed on the side of the hot water tank or inside your owner’s manual.

It will take a few minutes for the water heater to recover and bring the water back up to the right temperature. Reinspect the T&P valve one more time to make sure there are no leaks around the threads or from the discharge tube. Done!


Keeping your home and family safe from water damage is as simple as testing your water heater’s T&P valve regularly. Not sure if it’s working properly? When in doubt, change it out! Replacing a water heater relief valve is a quick and easy way to protect against a ruptured hot water tank. Plus, you can add another accolade to your DIY résumé.

Happy Plumbing!

Trevor Woods is the founder of Plumb University® and he started in the plumbing and construction industry in 1997. Since then, his mission is to make plumbing repair and maintenance easy for everyone. And each year, he continues to help more people with their plumbing installation, care, and troubleshooting.