Your Water Heater's Relief Valve: What It Is And Why You Should Check It Regularly

Both gas and electric tank water heaters have a safety feature called the temperature and pressure relief valve. Also called the T&P valve or PRV valve, this prevents pressure from building up to dangerous levels that could cause an explosion. 

How is an explosion even possible? As water is heated, it expands slightly. If for any reason, such as the failure of the thermostat, the water continues to heat past 212 degrees Fahrenheit, it will continue to expand and build pressure within the closed confines of the water heater's tank. Eventually -- although it would be rare -- the pressure becomes great enough that the tank itself explodes. The T&P valve prevents this from happening by releasing some of the pressure.

Why Do T&P Valves Fail?

There are a few reasons why a valve can stop working properly. In your water heater's tank, the most likely reason is that sediment has built up and is preventing the valve from opening as it should. This is more likely if you're on well water and your filtration is not good or is worn out. In other cases, the water itself is hard, which means it contains minerals that can lead to a build up. Rusty pipes can also send bits of rust and debris into the valve.

Less commonly, the spring-loaded lever in the relief valve can fail. These are typically very reliable but it can happen. You might notice leaking from the valve if this is the case.

How Can You Maintain the T&P Valve?

To prevent the valve from freezing up or leaking, it's best to follow your water heater manufacturer's recommendation for flushing and cleaning the tank. This is best to do on an annual basis, and will flush out sediment that remains throughout the tank. 

Because the entire flushing process is a bit more detailed than the typical homeowner may prefer to do, you can call your plumber or water heater technician to perform this maintenance that will extend the life of your water heater. Your plumber can also assess the condition of the water heater parts, including your valve. 

You can check just the valve yourself by opening it, as that will flush away any sediment that is only inside the valve. The issue here is that the valve must be plumbed to the outside of the tank in order to do this safely. Because opening the valve will release hot water and possibly steam that could cause injury, it must be plumbed properly to a discharge or drain line. If you have your plumber check the valve and drain line for safety, you can open it every time you check your smoke detectors (twice a year) to clear it out.

What Signs Indicate a Problem with the T&P Valve?

There are a few indications that there's a problem with either your valve or your thermostat, which may be allowing water to heat too much. 

  1. Water releases slowly from the drain line. If there's a bit too much pressure in the system, the valve may release a little water at a time. If this only happens once or twice, it's likely to be all right. But if it happens regularly, the valve may be failing or the heater itself may be producing too much pressure.
  2. Water releases quickly from the drain line. If you suddenly have gallons of water releasing, it's because the water was too hot. It's possible that the thermostat has failed and needs to be replaced.
  3. Whistling or rattling noise. Excessive pressure that's not being released by the valve can cause pipes to rattle a bit. You may also notice that when you turn on the shower, the water seems to flow very fast and then slow down dramatically. This indicates that the valve is not working and needs to be replaced.

If you have questions about your water heater's temperature and pressure valve, or any other parts on the heater, call a plumber, such as Miller & Humphrey Plumbing & Electric Inc, for a professional assessment.