Leaking Water Heater T&P Relief Valve? Do This

Why is My Water Heater Temperature and Pressure Relief Valve Leaking?

Every water heater has a temperature and pressure (T&P) valve installed as per the code. This allow it to discharge excess water/steam when the temperature/pressure of the water in the tank rises beyond the allowable limit.

Without the T&P the water heater is a potential bomb. When this valve starts leaking/dripping water all the time however, it is a sign that it is defective or there are other issues affecting the water heater.

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A leaking water heater temperature and pressure relief valve is a sign that it is defective, you have a closed-loop system (with a check valve or pressure reducing valve), or the water pressure in your house is too high. A waterlogged thermal expansion tank can also cause the problem.

If a new temperature and pressure relief valve is leaking after replacement, the problem is not with the valve. You either have a closed-loop system or the water pressure in your house is too high. Installing a thermal expansion tank or pressure reducing valve will fix the problem.

To fix a leaking temperature and pressure relief valve you will need to replace it with a new one. If you have a closed-loop system you will need to install a water heater expansion tank. A leak caused by high water pressure (above 80 psi) can only be fixed by installing a pressure reducing valve.

If you have a water heater expansion installed but still the temperature and pressure relief valve is leaking, there is chance that the expansion tank is waterlogged. In that case you will need to replace the expansion tank. Also make sure that the water pressure in your house is below 80 psi.

Troubleshooting and Fixing a Leaking Water Heater Temperature and Pressure Relief Valve

A leaking temperature and pressure relief valve is not really dangerous. It means that the valve is working as it should. It becomes dangerous when the valve does not leak/discharge pressure even when the temperature and pressure of the water inside the heater is above its rating.

In order to fix the leak on your T&P valve, you will need to first investigate why it is leaking in the first place. It is not always that when the valve leaks that a replacement is needed.

As I have already mentioned, whenever this valve is leaking it is either it is defective, the water pressure is too high or you have a closed-loop system. Fixing one of these 3 will solve the problem, but you have to isolate the problem first.

Here is how to go about it:

1. Do You Have a Closed-Loop System?

A closed-loop system means that water in your house can only flow in one direction. This is made possible by installation of a check valve or pressure reducing valve (PRV).

In the past, water from your house could easily flow back to the city’s water supply pipes if for one reason or the other the water pressure in your house increased than that in the city pipes. This is what is called backflow.

It was later discovered that water from homes used to contaminate the city water and currently water meters come with a check valve to prevent backflow. Check valves can also be installed in homes on existing pipes.

The reason this is a problem for water heaters is that when water is heated, it expands. When the water expands, it exerts more pressure and if the pressure exceeds the T&P valve rating (150 psi), the valve will start leaking/dripping until the pressure of water in the tank falls below the allowable level, or there is a hot water demand in the house.

In the past this was not an issue since expanding water in the water heater would just flow back through the cold water pipe. With a check valve or pressure reducing valve (acts like a check valve) in place that is not possible.

If you have a hot water recirculation pump in your home, you most definitely have a check valve. This check valve prevents cold water from flowing back to the cold water, making sure that you have instant supply of hot water.

Solution: Install a Water Heater Expansion Tank

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A water heater expansion tank, also known as a thermal expansion tank is a small tank installed on the water heater’s cold water supply pipe between the shut off valve and the water heater.

Most water heater expansion tanks have a capacity of 2 gallons (for a 50-gallon water heater) although bigger ones exist for big water heaters. The size of the expansion tank is also determined by the pressure of the incoming cold water.

A thermal expansion tank has a bladder/diaphragm in the middle, which allows it to have 2 compartments. The bottom compartment is filled with cold water while the top section is filled with air, whose pressure should be equal to that of the incoming cold water.

When the hot water in the water heater starts to expands, it flows back to the expansion tank and compresses the air in the top section. This is how the expansion tank prevents your water heater’s temperature and pressure valve from leaking.

If you are conversant with how water wells work, an expansion tank works like a pressure tank. People who use water from a well and have a check valve between the pressure tank and the water heater will also need to install a thermal expansion tank.

Water heater expansions tanks costs between $50 and $150 depending on size and brand. You will also need to buy a tee which allows you to install it on the cold water supply pipe. This one here is one of the best expansion tanks on Amazon.

Although you can install an expansion tank on your own, I would highly encourage that you get it installed by a licensed plumber. It is costly but safe. Some water heater manufacturers will actually deem your warranty claim void if they discover a plumber didn’t install the tank.

Below is a table of the different sizes of thermal expansion tank sizes needed for various sizes of water heaters at different water pressures. You can also get the expansion tank size calculator here.

2. Check the Thermal Expansion Tank

If you have a thermal expansion tank installed but still water is leaking from the temperature and pressure relief valve, either the tank is waterlogged or the air pressure in it is too low. Sometimes the bladder in the expansion tank ruptures, and as result the entire tank fills with water. When that happens, there will be no room for water expansion and water will be forced to leak from the T&P valve.

If the air pressure in the expansion tank is also too low, there will be hardly any water expansion taking place. As you know, water cannot be compressed and it will hence have to escape via the T&P valve.

So, how do you know if the water heater expansion tank is bad?

  • Take a piece of metal pipe and tap the expansion tank from top to bottom. If the expansion tank is waterlogged, it will sound quite solid from top to bottom. On the other hand, if the bladder is not ruptured, the top part will sound hollow.
  •  Remove the air inlet cap and try to bleed air from the tank. If air leaks out, then the bladder is intact. When you notice water coming out instead of air then the tank is waterlogged and will need to be replaced.
  • Connect a pressure gauge to the air inlet valve and check the pressure of the air in the tank. If the air pressure is lower than that of the incoming cold water, you will need fill it up with an air compressor or even bicycle pump.

3. Check the Water Pressure

If the water pressure in your house is too high, water will leak out from temperature and relief valve. Replacing the valve or installing a water heater expansion tank will not fix the problem. The only solution in this case is to first install a pressure reducing valve.

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So, how do you know that the water pressure in your house in your house is too high. Get a pressure gauge and connect it to a garden faucet (or any other faucet) with the same threads and turn on the water.

The normal water pressure in your house should be between 40 and 80 psi. If the pressure reading on the pressure gauge is above 80 psi, then it is too high.

Apart from causing a leaking T&P valve, high water pressure also causes premature failing of household appliances like dishwashers, washing machines and toilet fill valves. High water pressure can also cause water hammers and pipe vibrations around the house.

Most people are of the opinion that an expansion tank will solve the problem of high water pressure in the house. That is however not correct. The best thing to do is to install a pressure reducing valve and only then can you install an expansion tank.

If you would want a recommendation for a great pressure reducing valve check out this one on Amazon.

4. Replace the Temperature and Pressure Relief Valve

If you have a water heater expansion tank in place, and your water pressure is ok, you are most likely dealing with a faulty T&P valve. A faulty T&P valve will need to be replaced. It cannot be fixed.

Fortunately, replacing a water heater T&P valve is an easy task which you do not need to pay a plumber to fix for you. The only cost you will incur is that of a new valve which costs between $20 and $30.

The first thing to do is make sure that you buy the correct valve. Your old valve will have a tag with all the specifications. Write them down and buy a matching valve. Once that is done get down to work.

Here is how to replace a water heater temperature and pressure relief valve:

  • Turn off the water heater cold water pipe shut off valve.
  • If you have an electric water heater turn off the power at the circuit breaker. For a gas water heater turn off the gas pipe and turn off the pilot light.
  • Connect a garden hose to the water heater drain valve. The aim is to drain about 15 gallons. To know that enough water has been drained out, open the T&P valve and if no water flows out just know that the level of water in the tank is below it.
  • Position the end of the hose on a floor drain and open the drain valve using a flathead screwdriver.
  • Open the nearest hot water faucet. This will bring in air and hence quicker drainage.
  • Once enough water has drained out of the water heater, turn off the faucet and the drain valve. Remove the garden hose from the drain valve.
  • Disconnect the discharge tube using an adjustable wrench. The discharge tube is the vertical pipe connected to T&P valve.
  • Use the same wrench to disconnect the old valve from the water heater.
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  • If the threads look dirty, scrub them using a wire brush.
  • Wrap Teflon tape round the new valve’s threads and thread it on the water heater until hand tight. Tighten it using the wrench.
  • Connect the discharge tube and tighten it as well.
  • Turn on the cold water pipe shut off valve and also open closest hot water faucet.
  • You will notice the faucet spitting out air. Let it go on until there is a continuous and smooth stream of water and then turn off the faucet.
  • Turn on power/gas to the water heater and light the pilot

And basically that is how to replace a faulty and leaking water heater temperature and pressure relief valve.

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