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Why Is My Water Heater Whistling?

August 24, 2017

That whistling noise you hear is most likely your water heater’s temperature and pressure relief (TPR) valve opening to relieve extra pressure inside the water heater.

In this article, we’ll discuss:
  • How your TPR valve works
  • What causes excess pressure to build in your water heater

Need a plumber to fix this right away? Just contact us and we’ll send one right over.

How your TPR valve works

Your temperature and pressure relief valve (aka “TPR valve”) is designed as a safety mechanism to prevent your water heater from exploding in your home.

TPR valves are usually located on top of the tank or on the side of the tank. The valve is always attached to a discharge pipe that diverts hot water away from the heater.

You see, water expands as it heats up inside your water heater. Now, your water heater is designed to handle a certain amount of pressure. But if the temperature of your water is too hot, pressure builds to dangerous levels inside the water heater, risking an explosion.

That’s where your TPR valve steps in to save the day.

As soon as the pressure inside your water heater hits unsafe levels, that valve automatically opens to let out hot water. This relieves the pressure inside the tank (and often makes a whistling sounds as it does so).

But here’s the bad news: TPR valves often don’t open until pressure surpasses 150 psi (pounds per square inch). And even though your water heater can handle pressure around 150 psi, it’s not good for it (or your plumbing, for that matter).

So if your TPR valve is whistling and discharging water, you need to call a plumber ASAP to fix the problem.

“What’s causing too-high pressure in my water heater?”

Some water heater problems that can result in pressure build-up include:

Your temperature is set too high

Every water heater has a water temperature setting that can be adjusted. If the water temperature is set too high, though, it can eventually cause unsafe pressure inside the water heater.

What to do: Make sure your water heater temperature settings are well below 140 degrees F. In fact, the Department of Energy recommends keeping the temperature at 120 degrees F to save money and prevent pressure issues.

The exterior water supply is coming in at too high pressure

As water travels into your home from the municipal water supply, it does so at a fixed pressure. Anything over 65 psi is considered “high” pressure and can make the pressure in your water heater skyrocket.

What to do:Have a plumber check the incoming water pressure. If it’s over 65 psi, have them install a pressure reduction valve at the inlet to your home.

You have a defective thermostat

Your water heater thermostat should shut off the burners once the water reaches your set temperature. But if the thermostat is bad, it will allow the water to continuously heat until the pressure reaches unsafe levels, eventually triggering your TPR valve.

What to do: Have a professional repair or replace the thermostat. They may also need to replace your entire gas assembly (if you have a gas furnace).

Sediment is building up inside the water heater

Over time, “hard” minerals in your water (calcium and magnesium) settle to the bottom of your water heater and accumulate, creating a barrier between the water and your water heater’s burners. This causes your burners to stay on longer than they should, overheating the water and allowing pressure inside the water heater to build.

A tell-tale sign that you have sediment buildup is a popping, knocking noise coming from your water heater.

What to do: Have a professional flush your water heater to get rid of that pesky layer of particles coating the bottom of your tank.

Need help from a Denver plumber?

If your water heater is still whistling and you’re not sure why, contact us right away.

We’ll send over a plumber who can locate and fix the issue before any major damage occurs.

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