Is Your Water Heater in Danger of Exploding? This Test Will Tell You

April 16, 2016

And it has happened in homes from Utah to Australia.

But why? What causes a water heater to explode?

Will yours explode soon?

How can you prevent it?

We’ll answer all those questions here.

Side note: If your water hearing is making a knocking/popping noise, then that’s not a sign your water heater will explode. It’s a sign that your water heater is full of sediment and needs flushing.

Why does a water heater explode?

One word: Pressure.

You see, as the tank heats the water, its volume expands (this is called thermal expansion), increasing pressure inside the tank. It’s like how pressure builds up in a covered pot of boiling water.

If the pressure gets too high, it must be relieved in some way. Otherwise, the tank’s bottom will eventually give way, pushing the tank up, rocketing it straight through your roof.

Lift off! Source:

Thankfully, this amount of pressure rarely happens because your water heater has a T&P (temperature and pressure) relief valve


Its job is to release excess pressure, preventing your water heater from becoming a bomb.

When pressure in your tank reaches a dangerous level, here’s what the valve does:

  1. The white rod pushes a spring in the valve.
  2. The spring pushes the switch up.
  3. Water is released, lowering water volume and therefore lowering pressure in the tank.

Closeup of T&P relief valve. Source: Bradford White

Water being released through the valve’s discharge tube. Source: Bradford White

So you’re safe as long as your T&P relief valve works

Do this: Test the T&P relief valve

Step 1: Find your water heater T&P relief valve. It’s typically located on the top or side of the water heater.

Typical locations of a T&P valve. Source: Installation Instruction for Temperature and Pressure Valve

Step 2: Place a bucket under the valve’s discharge tube and put on some close-toed shoes to protect your feet from the hot water you’re about to release.

Step 3: Flip up and hold the T&P relief valve switch up for 5 seconds. Then let go and allow it to shut automatically. If water comes out the discharge tube, that’s normal.

If no water comes out the tube, or water leaks from the valve itself, that’s bad. That means the valve can no longer relieve your water heater of pressure, and you need to call a licensed technician to repair the valve ASAP.

If you don’t get it repaired, your water heater may explode.

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How to decrease pressure and maintain your T&P relief valve

Let’s assume the valve works just fine. Whew! Good. No explosions for you.

But you’re not out of the woods yet. The valve isn’t perfect and can wear down over time. So you need to do two things:

Keep pressure low by keeping temperature low — Make sure your water heater’s temperature stays around 120 to 125 degrees. Any higher than that can lead to scalding hot water and high pressure in the tank.

Maintain the valve by flipping it up twice a year — You may only have to check it once if you get annual water heater maintenance through a plumber because they’ll typically check and test the valve.

Need a Kansas City company to repair your water heater?

If you’re in our service area, we can help. Contact Santa Fe Air for a water heater repair.

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