Rush Plumbing & Rooter Water Heater Pressure Relief Valve

Rush Plumbing & Rooter What is a Water Heater Pressure Relief Valve?

A pressure relief valve is an installation commonly seen on water heaters as a safety mechanism in case of over-pressurization. Water heaters by nature take cold water and raise it in temperature. This leads to what is called thermal expansion which is essentially the phenomenon that occurs by which an increase in water temperature causes an increase in volume. In fact, for a 40 gallon water heater, the volume can increase as much as a ½ gallon.

So where does the water heater pressure relief valve fit into this equation? Well with the increase of temperature that causes thermal expansion, there comes an increase in pressure as well. This pressure builds up inside the tank and is expelled by any means necessary. Usually the extra water volume flows back out the cold water line coming into the tank, but if you have a check valve on the cold water line (as is more common nowadays for water safety reasons) then the pressure can’t be released and it is highly likely that an explosion will occur, ruining your plumbing and/or water heater. To avoid this from happening, water heaters come with a pressure relief valve which can relieve the water pressure harmlessly into your pan.

Water Heater Pressure Relief Valve

How Does Water Heater Pressure Relief Work?

Pressure relief valves respond to two things, temperature and pressure. If the temperature inside your water heater tank reaches 210 degrees Fahrenheit or reaches 150 psi, then the pressure relief valve is triggered and opens to release the pressure build-up caused by thermal expansion. There is usually a water pan underneath the water heater that catches the water released by the pressure relief valve.

Pressure Relief Valve Replacement

Sometimes a pressure relief valve needs to be replaced. Because of the water that goes through it, there can sometimes be carbon that builds up and creates problems within the pressure relief valve. Once a pressure relief valve has become defective, it needs to be replaced. Our plumbers at Rush Plumbing & Rooter have the tools and equipment necessary to safely remove and install pressure relief valves for every type of water heater.

If you notice a pressure relief valve dripping or leaking consistently, you may need to call in a plumber to determine the nature of the issue. There are a couple different reasons a leaky water heater pressure relief valve might be acting up. One, the valve could’ve just become defective because of carbon build-up. Two, the pressure relief valve is being repetitively kicked into operation because of persistent exceeding pressure within the tank (as in, the valve is working properly, but being over-used). For the former reason, you’ll need to get your pressure relief valve replaced. If you do this and you are still experiencing a leaking valve, then it is probably time to consider an expansion tank for your water heater system.

Expansion Tanks

Expansion tanks are small volume tanks that can be installed on your water line near the water heater as optional storage for increased water volume as the result of thermal expansion. They keep your plumbing system safe by reducing the demand that the increased pressure inside the tank presents as well as creating a better alternative than a pressure relief valve constantly pouring excess water into your water pan.


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