Generally, you let your hot water heater do its own thing in your basement: you don't bother it and it doesn't bother you. Chances are good that the most trouble it will give you is needing to be replaced every 10 years.

However, occasionally things go very, very wrong. If you have heard of a recent water heater explosion in your area, you may be nervous. You should know that this disaster is not likely to happen to you-but to calm your nerves, read this explanation for how it happens and how to prevent it.

What Can Happen?

When a water heater explodes, it's generally because the water in the heater was too hot, which puts the tank under too much pressure. When water gets hot, it expands, exerting pressure on the tank.

However, because there is not enough room to fully expand, the water cannot boil into steam, though at this stage the temperature is far past when water usually boils. The water stays in its liquid state, getting hotter and hotter and bigger and bigger.

Finally, the water will put enough pressure on the tank to rupture it. The hole in the tank will suddenly give the hot water room to expand, which means that it will instantaneously boil into steam. The steam takes up 1,700 times the volume of water, which means that the steam will suddenly, violently push out as it expands. This is called a BLEVE, or a boiling liquid expanding vapor explosion.

When a BLEVE occurs, it's usually an unexpected and dangerous event. The show "Mythbusters" has exploded water heaters with shocking effects: the explosion sent the water heater up 500 feet in the air. When this happens to a home instead of on a TV show, the effects can be devastating. Even a small explosion can cause thousands of dollars in damage, and a large one can destroy the entire home.

Why Does This Happen?

Two things cause most explosions.

1. Temperature

This is the most obvious problem: if your water temperature is set too high, it can cause a BLEVE. If the water never gets hot enough to boil, it will not rupture the heater. Set the temperature between 120 and 130 degrees Fahrenheit-as a reference, water boils at 212 degrees. If the temperature is above 130 degrees but below 212, the water heater will not explode, but your water may scald you.

If you set the temperature correctly but the control is broken, your water may reach dangerous temperatures. If you turn on a hot water faucet and steam comes out instead of water, take immediate action. If you have an electric water heater, turn off the power to it. If you have a gas water heater, shut off the gas valve. Then call a professional to deal with the situation.

2. Temperature and Pressure Relief Valves

These are also called T/P relief valves, and they are supposed to act as a fail safe. If the water gets too hot and exerts too much pressure, they let some water out to relieve the pressure. That way, the tank never has to explode. Malfunctioning T/P relief valves are the most common factor in water heater explosions. 

Sometimes homeowners or unlicensed plumbers may alter T/P relief valves in dangerous ways. If the valve leaks, you may be tempted to add something to it to stop the dripping. Some people add a cap or even a spigot that they can then turn off. This is very dangerous and defeats the purpose of having a T/P relief valve. If the valve leaks, replace it instead of modifying it.

How Can I Prevent Explosions?

The likelihood of an explosion is very small. However, you can do a few things to make the chances even smaller:

Every year, have your hot water heater inspected and cleaned by a professional. This maintenance will make sure that the controls and safety features work correctly.

At least once a year, test the T/P relief valve. Lift the lever or test handle to let water out, which shows that the valve works. Use a drain line to make sure that the hot water coming out does not scald you. You can find more information about the location and appearance of the T/P relief valve on this brochure made by the Washington State Department of Labor & Industries.

Check the capacity of the T/P relief valve. The valve's pressure setting should be below the water heater tank's working pressure. You can find this information on the T/P relief valve and on the water heater tank's nameplate.

No matter how good its condition may seem, replace the T/P relief valve every three years. This ensures the water heater's safety.

If you're not sure you can check the T/P relief valve on your own, a professional can help you.

Protect Your Home

Water heaters are very safe appliances. The odds are small that both the temperature control and the T/P relief valve will fail. And if you take care of your water heater, there is even less of a chance. If you're worried, contact C.B. Lucas Heating & Air Conditioning to help you out-then relax. Your home is safe.