Old Water Heaters Are Dangerous: Fact Or Fiction?

The water heater in your home is a large appliance that has the potential to cause much damage when things go wrong. Many people have heard that old water heaters can be significantly dangerous, sometimes even causing explosions. When it comes to old water heaters posing a danger, what is myth, and what is reality?

Old water heaters are dangerous, especially if they have not been well maintained. Mold growth, bacteria growing in sediment, critter infestations, bursts, and explosions are all potential dangers that old water heaters present for the homeowner. Old water heaters should be replaced for safety.

Nothing has an indefinite lifespan, including water heaters, but they are out of sight and often out of mind until they develop a problem. Water heaters that are close to their expected lifespan of 10 to 12-years could be ticking time bombs in your home. The danger an old water heater can present to your home can be anywhere from minor to catastrophic!

Do Old Water Heaters Pose A Threat?

All water heaters have the potential to cause problems and pose a danger in your home, but as the unit starts to age, the danger aspect begins to increase.

Most water heater manufacturers only guarantee water heaters for up to 5-years, even though the unit can remain in your home for up to 3 times longer than this timeframe! The failure rate of water heaters increases with age from less than 10% in the first 5-years to 12 percent in units between 5 and 10-years old. Water heaters that are over 15-years old have a 90% risk of failure, which means it is not a case of if your water heater will fail, but when.

Dangers Posed By Water Heaters

The potential risk of damage to your home and the risk of injury or health problems from a water heater can range from mild to severe. The damage a water heater can inflict on your home can result in costly repairs or insurance claims when the old unit fails.

The dangers that arise from water heaters, particularly old water heaters, can be summarized as follows.

Mold Growth

Mold growth is a particular problem for old water heaters that are located in basements. Leaking pipes, valves, connectors, and even the seams of the tank itself can create a moist environment where the mold can thrive and grow.

This can pose a serious health risk to everyone in the house and also cause the rotting of timbers and other structural components of the house. Because the water heater is tucked away and not noticeable, the problem may go unnoticed until it becomes a health risk of a home repair nightmare!

Mold is not the only undesirable growth that can result from a leak in an old water heater. Fungi can also grow in this environment, and the spores they release can cause health and respiratory problems for the residents of the house.

Sediment Build-Up Allowing Bacteria Growth

Sediment in the form of lime of calcium carbonate can build up over time on the inside of the water heater tank. This mineral is naturally found in some areas where tap water has high mineral content.

The sediment build-up causes two problems. The first one is that the sediment provides a location in a warm moist environment for bacteria to thrive, and yes, you get heat-resistant bacteria. When you combine this bacteria-friendly environment with our next point, critter infestations, you can see where the bacteria may come from.

The bacteria growing in the sediment has the potential to make you and your family sick from using the contaminated water.

The second problem from sediment build-up is that the lime in the water can also provide a corrosive environment that can eat away the metal from the inside of the water heater. This can lead to bursts or explosions in old water heaters as the metal becomes too weak to hold the pressure.

Water Heater Critter Infestations

Rats and mice and cockroaches are the vermin we speak of here! These creatures are all carriers of disease and have a penchant for nice warm spots to make their nests and breed.

Water heaters provide the perfect level of warmth and shelter for them to make their nests. Often the location they choose is close to the burners on gas water heaters, which also poses a fire risk.

The critters also defecate and urinate around where they are nesting, which adds to the health risk and bacteria growth around the water heater. Rodents may not be able to enter the water heater tank, but their urine and feces can leech into older tanks through valves and vents.

The mice and rats chew on electrical wires and gas pipes, resulting in gas leaks or electrical short circuits, which are a real danger to all who live in the home.

Cockroaches are the ones that are more problematic when it comes to them actually gaining entrance into the tanks. They are small enough to crawl through older valves and vents and end up inside the tank. This is the tank containing the hot water you shower in, wash dishes in, and cook with!

Water Heater Bursts

Many old water heaters do not have safety valves, as these were not the standard when the old water heater tanks were manufactured and installed.

As these types of tanks get older, they can suffer from blocked valves, or overheating, which can increase the pressure inside the water heater. The increased pressure can reach the point where the metal structure of the tank ruptures and the hot water pours out all over your basement or ceiling, depending on where the tank is located.

A burst like this can pose a danger from the scalding hot water, particularly if the water heater is located in the roof space. The other danger that this can cause is significant water damage to your home, your furniture, and your belongings.

Water Heater Explosions

While it is a rare occurrence, the risk of a water heater explosion is a possibility, and the risk increases the older the water heater is.

There have been reports of water heaters exploding through two stories or launching themselves through the roof and up to 500-feet in the air.

This type of catastrophic event could be life-threatening for people in the house, not to mention the damage the home would sustain from this type of water heater explosion.


Old water heaters are not only potentially dangerous, but they are also inefficient and can increase the costs of your utility bills. It comes to a point in every water heater’s life that they are simply not worth the risk or the trouble and extra expense and should simply be replaced!

Regular maintenance will help extend the water heater's life and minimize some of the potential dangers. However, if your aging water heater is older than 10-years, you should pay close attention to its condition and possibly look at replacing it as a preventative measure, even if it is still operational.

Newer models make use of modern technology, making them safer and more energy-efficient!