How to Replace a Water Heater Relief Valve: DIY Installation Tips

Water heater temperature and pressure relief valve (TPR)Water heater temperature and pressure relief valve (TPR)

Is your water heater relief valve dripping or leaking because something made it open and stay open?

Since working on the TPR and "trying" to repair it is not recommended, let's see how to replace a water heater relief valve and keep the heating process at a safe level.

What is a water heater relief valve, and how does it work?

A water heater temperature and relief valve or TPR (or T&P relief valve) is a safety device that is temperature and pressure sensitive and designed to limit its levels in tank-type heaters. A pressure relief valve is also required on tankless water heaters per ANSI and CSA standards.

Whenever there is a call for water heating, electric heating elements or a gas burner (depending on the type) turns on and starts heating stored water (tank-type heaters). 

Once the temperature reaches the set level, the unit automatically shuts down utilizing the thermostat and control valve. If for any reason, the thermostat or control regulator quits working and fails to stop, the temperature and pressure reach dangerous levels.

The dangerous level is when the water is heated beyond its boiling point of 212 F. The overheated water turns into steam instantly, increases its volume, and releases the amount of energy enough to become a steam-powered bomb. This is why the heater, working without the safety elements, can weaken the tank, cause rupture, and even explosion.

Why is my water heater relief valve leaking?

All tank-type heaters, whether heated by gas, oil, or electricity, must have a TPR valve to prevent an excessive increase in the temperature and pressure within the system.

Once the relieving point of the relief valve is reached, it releases the excess pressure with the hot water and allows cooler water to enter the tank and lower the temperature.

The T&P regulator has a probe immersed in the first six inches of the water heater to measure the stored water temperature. The temperature rating is set to 210 F.

As the probe senses an excessive temperature (i.e., due to thermostat failure), the relief valve opens fully and discharges hot water until the temperature is below its reset value.

The maximum working pressure in the water heater is up to 150 psi (it can be found on the water heater's data plate), and it should never be above the allowable working pressure stamped on the water heater relief valve.

When the pressure in the tank reaches the pressure rating, the water heater pressure relief valve opens to release the water.

Many homeowners would see this process as leaking, but this is normal. This is also known as dribbling or weeping in the plumbing and HVAC world.

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Installing water heater parts for the safe operation

It is recommended to install an expansion tank if the water heater relief valve releases water after a large amount of hot water is used. What happens is that the backflow-preventer valve or a pressure regulator is probably limiting water expansion, therefore causing the TPR to open.

Note: An expansion tank should take care of excess hot water and pressure built but not released through the TPR regulator.

A TPR valve must comply with the ANSI and ASME codes, certified by a nationally recognized testing lab, correctly sized, and adequately installed.

Due to overheating and extreme tank pressure that can cause serious injury, it is mandatory to install a T&P safety regulator and keep at its designated opening and never altered, restricted, or blocked. No obstruction is to be placed between the relief valve and the heater.

It is vital to have the BTU capacity of the TPR exceed the BTU input of the heater.

When installing a water heater relief valve, position it downward and install the tubing to discharge the excessive water. The discharge pipe should be appropriately sized and terminated to an adequate drain (6" above the floor drain or drain pan) with no contact with the electric part.

How to test a temperature and pressure relief valve

The opening for the temperature and pressure relief valve is either on the side or on top of the heater tank. The recommendation is to install the brand-new water heater relief valve only.

To prevent any problem with a water heater relief valve, it must be manually tested at least once a year.

Note: When testing the relief valve, make sure no one is in front or around the outlet of the TPR valve discharge line, as the water from the tank might be very hot.

If a water heater relief valve fails to reset completely after lifting the lever and continues to release hot water, turn the unit and water off and replace the element.

If you see a puddle of water around the unit's base, a leaking water heater relief valve might be one of the causes.

Usually, water is seeping around the valve-tank connection, leaking at the threaded portion of the water heater relief valve connection and directly from the valve in moderate or large volumes.

A solution for these problems is to remove the relief valve and reseal connections if the problem is on the threaded part or to replace this part entirely.

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How to replace a water heater relief valve - Installation tips

  • Apply the Teflon tape or approved pipe sealant on threads and install a water heater relief valve in the marked opening. The valve must be installed, so the temperature-sensing element is immersed in the water within the top 6" of the tank.
  • Connect a drain pipe to the valve outlet and run it to a safe place for water disposal. Keep the length as short as possible with the same size as the valve connection.

Also, when replacing a T&P valve, do the following:

  • Turn off the power and gas supply.
  • Shut off the water supply.
  • Drain the tank, so the level is below the TPR valve.
  • Unscrew the old TPR valve.
  • Apply the Teflon tape or appropriate pipe joint compound on the thread.
  • Put the discharge pipe back.
  • Turn the unit on and refill the tank.
  • Restart the heater.

What to do when a relief valve is dripping?

There are two reasons why the temperature and pressure relief valve is dripping.

The water heater relief valve is dripping when it opens due to excessive temperature and pressure. In such a situation, water expands its volume, and if the system is closed, water cannot go anywhere except through the TPR valve and out.

The second reason for the relief valve discharge is when it is broken (faulty). The valve might not seal properly, so it gets stuck due to sediment buildup and remain open.

The problems with the leaks can be as small as wasted water and energy to severe, such as property damage.

In order to prevent damages from the water heater relief valve leak, it is recommended to install a discharge pipe. One end of the pipe is connected to the TPR valve, while the other end should terminate a few inches above the floor drain or a pan. 

Some experts do not recommend the termination of the discharge pipe into a home drain or outside because it is essential to see and monitor when the discharge occurs so there is time to react and deal with the problem.

The best way to prevent the TPR valve from opening due to increased pressure and temperature is to install an expansion tank on the plumbing system. This applies to closed systems.

Check if a TPR valve is sized correctly because the risk of explosion is real

A TPR valve is both pressure and temperature-sensitive, so when installed, it provides needed protection against extreme pressure and temperature, including rupture and explosion.

If the water inside the tank reaches boiling point (212 F), the water turns into steam, increases its volume, and releasing a considerable amount of energy, making the operation unsafe for the water heaters and surroundings.

When the TPR valve is correctly installed and working as it should be, and if the pressure and temperature go over the limit, the valve will discharge the overheated water. At the same time, cold incoming water enters, reducing the inside pressure and temperature.

If the BTU capacity of the TPR is lower than the BTU of the heater, the valve won't be able to do its job correctly, increasing the risk of the tank rupture or even explosion.

To make sure that the size is right, check the capacity found on the valve plate.

Note: Gas water heaters use BTU for the gas input or power, while electric models use kW. So, to convert kW to BTU, use this formula: 1 watt=3.413 BTU/hr. If the heating elements have a power of 5500 watts, this will give you 5500*3.413=18771 BTU/hr.

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