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What is the water heater pressure-relief valve and what purpose does it serve?


Year after year, your water heater serves an important role in your home. Your morning routine just wouldn’t be the same—or nearly as comfortable—without hot water. Yet, water heaters and their components do not last forever. Preventative maintenance is the key to ensuring that your water heater continues to safely provide your home with hot water. In this article, we’ll review a critical safety component of your water heater, the water heater pressure-relief valve.

We’ll discuss what it is, what it does, and how to ensure it’s still working and protecting both your water heater and your home.

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What is the water heater pressure-relief valve?

The name is actually quite literal. It’s a valve that relieves excess pressure in the water heater tank. By doing so, it can prevent excess pressure buildup that has the potential to cause a tank burst and flood your home. It’s an unheralded but essential safety mechanism for your water heater.

1. Role and Function:

When functioning properly, the pressure-relief valve will open to discharge excess water and release the increased pressure within the tank. This is essential because if the pressure or temperature rises above the safe threshold and the valve fails to operate correctly, it could lead to a water heater explosion.

2. Location:

The pressure-relief valve is typically located on the top or side of the tank. It includes a discharge tube that extends to about six inches above the floor. This tube is designed to safely discharge water in case the valve is triggered.

3. Operation:

The valve opens when the pressure inside the tank exceeds the preset limit, usually 150 psi (pounds per square inch), or the temperature goes above 210 degrees Fahrenheit. Once opened, it allows the excess heated water to flow out of the tank, lowering the internal pressure and temperature.

What leads to excess pressure in the tank?

As your water heater heats up the water in the tank, the water expands and steam is generated. The greater the heat, the more expansion that occurs. This expansion puts pressure on the exterior walls of the tank, but this is to be expected. Some degree of excess pressure escapes through the water pipes connected to the water heater. In the event that it cannot, the pressure-relief valve triggers. By releasing some of the hot water and air, the valve lowers the pressure back down to safe levels.

For reference, the normal pressure of the water inside of the water heater tank is 50-100 PSI.

What can go wrong?

Various issues can occur with the pressure-relief valve on a water heater. These problems can potentially lead to dangerous and costly scenarios, such as an explosion or flooding. Here’s a detailed breakdown:

1. Pressure Buildup:

The primary role of the pressure-relief valve is to release excess pressure in the water heater tank. If the valve fails to do this, pressure can continue to build past safe limits, typically around 150 PSI (pounds per square inch). While the tank is designed to handle substantial pressure, there is a breaking point at which the tank can no longer contain the pressure and bursts. This is not merely a rupture; it can be a violent explosion, launching the tank like a missile and causing significant damage.

2. Flooding:

When a water heater tank bursts, it releases a large volume of hot water. If the heater is equipped with an emergency shut-off valve, this device will detect the burst and automatically shut off the water supply, mitigating some of the damage. However, without this emergency shut-off, the resulting flood can cause extensive and expensive water damage to a home or building.

3. Valve Failure:

The pressure-relief valve can fail for several reasons. It may become stuck or ‘frozen’ due to rust, corrosion, or mineral deposits building up inside the tank and on the valve components. This buildup can prevent the valve from operating correctly. In other cases, the valve may remain stuck after releasing hot water during a previous pressure surge.

4. Neglect:

A faulty pressure-relief valve may not be immediately noticeable to homeowners unless they regularly inspect and maintain their water heater. This lack of attention can allow problems to develop and escalate unnoticed.

5. Regular Testing and Maintenance:

Regular testing and maintenance are crucial to prevent these issues. The pressure-relief valve should be checked periodically, and the tank should be flushed at least once a year to remove any sediment build-up. If the valve is faulty or stuck, it should be replaced promptly.

6. Valve Replacement:

Homeowners should replace the pressure-relief valve every few years, or as recommended by the manufacturer, as a preventive measure. The frequency of replacement may need to be increased if the water heater operates under harsh conditions or the water supply is particularly hard or corrosive.

Quick Note

On the renowned TV series “Mythbusters,” an experiment examined the scenario of a water heater’s potential explosion when its safety mechanisms, such as the pressure regulator, were tampered with, leading to over-pressurization. The team conclusively demonstrated that a 50-gallon tank exploding could be lethal to individuals nearby, highlighting the critical importance of safety devices and precautions. Thanks to one of our readers, David Miller, for sharing this video with us on our Facebook page.

Testing the valve

We recommend that homeowners here in Chicago test their pressure-relief valve when they flush out their water heater twice every year. Bundling your water heater maintenance tasks together makes sense, since each of these tasks takes about 10 minutes to complete.

Start by positioning a large bucket underneath the valve. You are going to release some hot water during this process, so you want to make sure you’re wearing safe clothes to reduce a scalding risk. Remove the drain pipe attached to the pressure valve.

Then, gently lift the valve switch so that hot water begins to come out of the valve and into the bucket. For the purposes of this test, don’t push the switch all the way up.

Here’s a helpful, detailed guide from Family Handyman magazine on how to flush and drain a water heater.

Here’s how to test your water heater pressure-relief valve.

Watch the video below for a step-by-step guide to testing the water heater pressure-relief valve. If, at any point, you do not feel comfortable doing this, please contact us so we can send a plumber out to help you.

So long as water and air are coming out of the water heater during this test, your water heater pressure-relief valve is working as intended. On the other hand, if you’ve flipped the switch up and you’re not seeing any release, that could indicate a problem with the valve.

You should call our plumbing team at King immediately for service so that we can diagnose the problem and replace the valve, if need be.

What impact does water pressure have on your home?

Did you know that most people use between 80 and 100 gallons of water every day? From using the restroom and showering to cooking and cleaning, your water usage is a crucial part of your daily home routine. Here are just a few daily tasks most homeowners do without thinking, and the corresponding amount of water it takes to complete them:

Flushing a toilet: 1-3 gallons per flush

Showering: 17 gallons per shower (8-minute average shower)

Dishwasher: 4-6 gallons per cycle

Washing machine: 5-30 gallons per cycle, depending on your machine’s efficiency

This doesn’t take into account washing your hands, taking a bath, or watering your lawn. Your water use may also skyrocket during the summer, when you’re drinking more water or cooling off in the sprinklers.

Taking all this into account, it’s crucial that your water systems are working at their full capacity. Your water heater delivers hot water to your home, and your water pressure needs to be sufficient for your appliances to work and for your showers to be comfortable.

For all your daily tasks to run smoothly, water pressure is especially important. Imagine not having enough water pressure to flush a toilet or take a shower. There are other consequences to having water pressure that is too high.

To get your water pressure checked and adjusted by a professional, call the team at King Heating, Cooling, & Plumbing in Chicago, Illinois. We’re the experts on all home systems and can make sure your home is running at 100% capacity.

Low water pressure

It’s been a long day at work, and you want to come home, take a hot shower, and relax with the family. You turn on the shower to see a small stream of water—or droplets—coming from the shower head. Even when you turn the shower handle to full capacity, only a small amount of water drips out. What’s the problem?

Your water pressure is likely too low. This can be an annoying setback for many homeowners, who depend on high water pressure to shower, clean, cook, and more. How can you properly shower or wash your hands when only a few drops are coming out of the faucet?

High water pressure

On the opposite side of the water pressure spectrum, high water pressure can pose a danger to you and your family inside the home. When water pressure is too high, pipes can become damaged and systems can overwork themselves to bring that water to you. It’s just like the tale of Goldilocks and the Three Bears: you don’t want your water pressure too low or too high—you want it just right.

Low water pressure is usually just a nuisance to homeowners and doesn’t pose a serious problem. High water pressure, on the other hand, can damage fixtures, seals, joints, and more. Water pressure that’s too high can also waste a lot of water in the home, leaving you with a higher utility bill at the end of the month.

Getting to comfortable water pressure

As it comes from the municipal water supply to your home, residential water generally ranges from 40 to 80 PSI (pounds per square inch). Anything above or below this range could be considered too low or too high. Some experts will say that any level above 60 PSI is too high of water pressure for your home. It’s best to speak with a professional plumber to get your water pressure checked and to learn more about what level is right for your home. Your PSI range can be affected by elevation, house size, water needs, age of your home, and other factors.

If you haven’t checked your water pressure level in a while, it may be time to call King for a free VIP plumbing inspection. Even if you feel your water pressure and water heater are working great, there could be hidden efficiency problems lurking underneath the surface, such as a water heater that is running too hot and wasting energy. Only a true plumbing professional can get to the bottom of the issue and help you save money, month-over-month. If you are thinking about getting a new one, check out this article about when you should consider buying a new water heater.

We’re here for your plumbing and water heater needs

This goes without saying, but if you’re not comfortable flushing your water heater or checking the valve, don’t just ignore this crucial maintenance need. Give our team a call and have us out to your home to perform this service for you. Remember, this preventative maintenance can help prevent a tank burst and major water damage.