A leaking temperature and pressure (T&P) relief valve on your water heater can be a perplexing problem. Understanding why your valve is leaking ‒ and how to fix it ‒ are both important pieces of information for any homeowner to have.
So, why does my water heater pressure relief valve leak? There are numerous possible reasons your water heater’s pressure relief valve leaks; 1) either the water pressure inside the tank is too high, 2) the water temperature is too high, 3) the T&P valve hasn’t been used in a few years, 4) the wrong T&P valve was installed, or 5) the T&P valve itself has failed.
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Identifying the cause of your temperature & pressure relief valve leak may take a bit of time, but you should be able to figure it out without too much trouble. The rest of this article will take you through each of the possible causes of your leak and explain how you can fix each of them.
The Purpose of the T&P Valve
Before we get started, I just want to give a quick refresher on what the T&P valve actually does. This valve exists to give water and steam the chance to escape when the temperature or pressure gets too high inside the water heater tank.
Although the name contains both “temperature” and “pressure”, most valves are almost exclusively used for pressure relief. This is because the temperature of your water needs to rise to a ridiculously high level to set off the valve.
If this valve didn’t exist, your water heater would be a ticking time bomb sitting in your home. If excess pressure rose to an unsustainable level, the water heater could explode.
While settings can vary between different brands and models, the valve is typically set to open when the temperature exceeds 210 degrees and the pressure exceeds 150 psi. If your valve is set to a different set of specifications, you might have a valve intended for a different appliance.
High Water Pressure
Although many people automatically assume a leaking valve is a broken valve, that isn’t always the case. If your T&P valve is leaking constantly, there’s a good chance it’s working exactly as intended and is relieving excess temperature or pressure inside the water heater.
Testing the level of pressure in your water heater is a relatively simple process. You just need to buy a pressure gauge (available on Amazon) and attach it to your system of pipes. Don’t worry about whether you connect it to a hot water pipe or a cold water pipe ‒ both will show the same pressure.
While there are plenty of locations at which you can connect the gauge to your plumbing, the easiest option is to connect it to one of your outdoor hose faucets. You’ll need a pressure gauge with threading designed for garden hoses ‒ the one linked above has this feature.
With all other faucets and water outlets turned off, the pressure should be between 40 psi and 80 psi. If the gauge shows the pressure is at 150 psi or greater, excessive water pressure is probably causing your pressure valve to leak. But if the leak is active while the pressure is normal, the water pressure in your plumbing system probably isn’t causing it.
Excess pressure is usually caused by a closed plumbing system. The water heater does its job and heats the water, which causes upward expansion of the water and an increase in pressure. If the system is closed, the water won’t have anywhere to go, and the T&P valve opens to relieve the pressure.
You can typically solve an excess pressure problem by installing an expansion tank, which will give the pressure an outlet that isn’t the T&P valve. Expanding water can flow into the expansion tank instead of exiting via the T&P valve, and the water heating process can continue to work normally.
If installing an expansion tank doesn’t solve the problem, the tank may have been installed incorrectly.
High Water Temperature
The T&P valve opens for both excessive pressure and excessive temperatures. I admit, it’s extremely unlikely that the pressure valve is being set off by excessively high temperatures, as the water temperature would need to be near the boiling point to set it off. That being said, it’s still a possibility, so it would be wrong not to cover it here.
Checking the temperature of the water in your water heater is a simple and straightforward process.
- Get a meat thermometer.
- Turn on a hot water faucet.
- Run the hot water for a minute.
- Take the temperature of the water with the thermometer.
The temperature of the hot water coming from your faucet should be around the 120-degree mark. Anything more is dangerous, but still wouldn’t necessarily explain a faulty pressure valve. As I said, the temperature would need to be near the boiling point of 212 degrees to set off the valve.
T&P Valve Not In Use
If your pressure relief valve hasn’t been opened in a few years, a slight leak may spring after you finally open it. This leak usually isn’t anything serious ‒ a minor drip is the most it will likely become. If the leak does become more serious, you’ll have to replace the whole valve.
Unfortunately, the damage caused by years of non-use can be tough to fix. While I did say replacement was only required for serious leaks, the easiest way to solve even minor dripping issues is to replace the valve entirely. This way you don’t get your time and energy caught up in the intricacies of repairing something that costs less than $15 to replace entirely.
The Wrong T&P Valve Installed
This is a pretty uncommon cause of pressure valve leakage, but it is still possible. Other appliances ‒ like boilers, for example ‒ also use pressure relief valves. While these valves operate in the same way as the one on your water heater, they’re set to go off at a much lower psi. Boiler pressure valves typically release water and steam at 30 psi, not the 150 psi typical of water heater valves.
The reason this is extremely unlikely is that the valve would have been leaking from the moment you installed it. If there has been any time at all in between the installation of your water heater and the moment your valve started leaking, you almost certainly have the right kind of valve installed.
Failed T&P Valve
The final possibility is that the valve has failed and is in need of replacement. While T&P valves are usually pretty sturdy, improper installation or excessive wear over time can cause the valve to break down and spring a leak.
Fixing the valve is technically possible, but replacing it is honestly the easiest and safest option. Most replacement T&P valves cost approximately $30 or less, and the replacement process is pretty easy. Here’s a step-by-step walkthrough:
Replacing Your T&P Valve
What you will need:
- Large adjustable wrench or pipe wrench
- Flathead screwdriver
- Teflon tape
- Pipe dope
- Replacement T&P valve – See below
- Garden hose
Insider’s Tip: The video references Teflon tape, but I recommend Teflon tape with a thin coat of pipe dope over the tape for a watertight seal.
When purchasing a new T&P valve, you need to be sure you are purchasing the correct type. There are two types:
- Short shank
- Extended shank
The T&P valve with a short shank like the Camco 10471/10473 3/4″ Temperature and Pressure Relief Valve with 4″ Epoxy-Coated Probe fits most all water heaters that have a short shank. The valve will sit close to the tank in most cases.
The T&P valve with an extended shank like the Camco 10493 3/4″ Temperature and Pressure Relief Valve with 4″ Epoxy-Coated Probe – Extended Shank fits most water heaters that have an extended shank. The valve sits off from the water heater or sometimes the extended shank is needed to reach the inner tank.
Step 1: Turn the power off
The first thing we need to do it turn the power off.
If you have a gas-powered water heater, you need to shut off the gas supply. Now the video references turning off the gas and the control knob. You don’t need to turn the gas all the way off. You only need to turn the control knob to the vacation or pilot setting. This turns off the burners inside the water heater but not the pilot light.
If you are more comfortable turning off the gas, by all means, do so. If you do you will need to relight the pilot upon completion.
If you have an electric water heater, you’ll need to locate the 220 circuit breaker for the water heater and turn it off. This is needed to prevent the water heater from continuing to produce hot water while working on the water heater. We will also be partially draining the water heater and you don’t want the upper element to not be submerged in water.
Step 2: Turn the cold water supply off
Locate and close the cold water shut-off valve entering the water heater. This is usually located directly over the water heater. It will either be a ball valve or a gate valve.
For a gate valve, turn the valve clockwise to close.
For a gate valve, turn the handle perpendicular to the pipe to turn the valve off. If the valve is in line with the pipe, the water is on.
Step 3: Drain about 10 gallons from the water heater
Next, we need to drain the water level beneath the valve, this will be about 10 gallons of water from the tank. To do this, connect a garden hose to the drain valve located at the bottom of the water heater. Direct the garden hose outside or to a floor drain.
Open the drain valve on the water heater then open the hot water tap at a nearby sink to release the vacuum on the tank. Place a bucket under the discharge pipe connected to the valve to collect any water and open the T&P valve. When no water exits the discharge pipe from the T&P valve, close the drain valve and remove the garden hose.
Step 4: Remove the temperature & pressure relief valve
You will need to remove the discharge pipe from the existing T&P valve. Unscrew the pipe and set aside to reconnect later. You may have to cut the pipe off in some instances.
When the discharge pipe has been removed, use the large adjustable wrench (or 18″ pipe wrench if you need more leverage) to unscrew the old T&P valve. You will initially need to use some force to break the seal.
Remove the old T&P valve.
Step 5: Install the new T&P valve
Clean the inlet with a small wire brush. Wrap the Teflon tape around the threads of the new T&P valve in a clockwise motion. I like to use a thin coat of pipe dope as well before installing it. This will prevent leaks.
Screw the new T&P valve in by hand then use the wrench to tighten. Be sure the T&P valve is pointed downward.
Reattach the T&P valve drain pipe ‒ wrap the threads in Teflon tape before you do this. If you had to cut the pipe off, you’ll need to replace it with a pipe that is specifically rated for hot water use. When you glue the pipe back on, make sure to use glue that is also rated for hot water use.
Step 6: Turn the water on
Now that the T&P valve is tight and the discharge pipe is installed, we can re-open the cold water cut-off valve to refill the tank. Wait until all the air has exited through the hot water tap then we can close the hot water tap.
Step 7: Turn the power back on
Check for leaks or dripping around the repaired valve. If the repair went smoothly, everything should be dry.
Once you’ve confirmed everything looks good, turn the breaker at the electrical panel back on. For gas models, turn the pilot back on and adjust the temperature to the desired setting. If you turned the gas off, you’ll need to light the pilot light.
If you’ve exhausted all of the other possibilities mentioned in this article, replacing your T&P valve is is probably the best solution. If you prefer, you should contact a licensed plumber for the replacement of your temperature & pressure relief valve.
Are water heater expansion tanks required? Most cities require residential plumbing systems to be closed water heater systems. When a new water heater is installed on a closed system, an expansion tank is required by building codes. For more info see our article Are Water Heater Expansion Tanks Required.
Is a drain pan required under a water heater? In most cases, Yes. Whether you need a drain pan under a water heater is mostly determined by the location where it is installed. If your water heater is installed in an attic or ceiling space or inside the interior living space, a drain pan is required under your water heater. Drain pans are not required under the water heaters installed in garages in most states. For more info see our article Is a Drain Pan Required Under A Water Heater.
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