Can Water Heaters Explode? Causes, Warning Signs, & Prevention


water heater explosion

People have become accustomed to the convenience of having hot water in their homes. What most don’t realize is that a water heater can be a ticking time bomb waiting to explode. A neglected water heater could explode destroying their home in the process.

So can a water heater really explode? Electric and gas water heaters can explode if the pressure inside the tank is too high, failure of the temperature & pressure relief valve, or improper installation. With gas water heaters, flammable vapors or a gas leak can cause an explosion if a spark were to ignite the gas or flammable vapors.

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The risk of explosion in modern water heaters is minimized through various safety features. However, most water heaters are not maintained well and the risk is still present and very real.

Modern water heaters are equipped with a safety feature called the Temperature & Pressure Relief Valve (T&P Valve). These valves require service to stay in proper working condition.

In this article we will examine:

  • The 3 main causes of water heater explosions – the three main factors that cause water heaters to blow up.
  • 3 warning signs your water heater may explode – three signs that your water heater is in need of service and at risk of an explosion.
  • 7 ways to prevent your water heater from exploding – Seven things you can do today to make sure your family is safe from a water heater explosion. 

3 Main Causes of Water Heater Explosions

There are three main causes of water heater explosions. These are high pressure, gas leaks, and improper installation. Let’s look closer at each of these. 

High Pressure Inside the Water Heater

High pressure inside the water heater can affect both gas and electric water heaters. High pressure occurs when the water inside the tank is heated. As the water heats up it expands building pressure inside the tank. 

So what can cause high pressure to buildup inside the tank:

  • A temperature & pressure relief valve that fails to open and release pressure
  • A failure of the high limit switch on the upper thermostat
  • A water heater that has not been properly maintained

Failure of a Temperature & Pressure Relief Valve

tpvalve

If water pressure inside the tank becomes too high it is released through a safety feature called the temperature & pressure relief valve or T&P valve. All modern water heaters are equipped with this safety feature. However, some older water heaters do not have this feature.

If the temperature and pressure relief valve fails or is blocked the pressure has no way to release resulting in your water heater eventually blowing up. As the water inside the water heater heats up it begins to expand. If the pressure from water expansions and gets too high the T&P valve opens to release pressure.

Failure of the High Limit Switch

The high limit switch is a large red button located above the upper thermostat. If the thermostat is not regulating power to the heating elements, the water temperature will continue to rise to an unsafe level. The high limit switch will trip to cut power to the water heater thermostat and heating element.

The high limit switch located on the upper thermostat and is designed to trip in the event water inside the water heater exceeds 180 degrees. However, if the high limit switch were to fail to trip, the pressure inside the water heater could cause the water heater to explode due to increased pressure.

This is a highly unlikely scenario, as it would take a 1-2 punch of the high limit switch failure and the failure (or blocked) temperature and pressure relief valve to occur at the same time. This is a highly unlikely scenario. However, older water heaters may lack one or both of these safety features.

Lack of Water Heater Maintenance

As your water heater ages, minerals deposits in hard water begin to buildup inside the tank. This sediment settles at the bottom of the tank. Left unattended, this sediment hardens and will eventually corrode the inner lining, thus weakening the walls of the water heater.

As the walls inside the water heater tank weaken they become susceptible to explosions even under normal pressure levels that may not trigger the T&P valve or high limit switch.

Fortunately, with routine water heater maintenance, you can solve these problems and even double the lifespan of your water heater. See our article Water Heater Maintenance Tips to 2X Your Tanks Lifespan.

Flammable Liquids, Natural Gas, or Propane Gas Leaks

This only affects natural gas or propane-powered water heaters. Electric water heaters do not have a gas supply and do not utilize open flames to heat water. 

Gas and propane-powered water heaters have an incoming gas line, internal gas lines, and fittings where gas leaks can develop. A gas leak can be identified by a “rotten egg” smell coming from around the bottom of the water heater.

Natural gas and propane actually is colorless and odorless gas. A harmless chemical called mercaptan is added to give gas a distinctive “rotten egg” smell. This helps homeowners identify when a gas leak is present.

If a gas leak develops in or around the water heater, even a small ignition flame or electrical spark can ignite the gas causing a massive explosion.

The same is true for other flammable liquids often stored in garages like gasoline, kerosene, paint thinner, and other solvents which can be ignited accidentally by the pilot light of a gas water heater.

All gas or propane water heaters should have a gas detector nearby. We recommend the Kidde AC Plug-in Carbon Monoxide and Explosive Gas Detector Alarm.

Improper Water Heater Installations

Many homeowners like doing things themselves. It’s good to save money on home projects. However, unless you have plumbing experience you should leave water heater installations to a licensed plumber.

Some of the improper installations we see include:

  • Gas water heaters not installed on the proper 18″ stand. The purpose of the water heater stand is to get the ignition source off the floor where other flammable liquids may be stored.
  • Gas water heaters installed in garages without a stop post to prevent cars from hitting the water heater and causing an explosion.
  • Gas lines without drip leg sediment traps. Drip leg sediment traps help to prevent sediment from clogging gas lines and inlets at the water heater. Many gas lines on older water heaters commonly do not have a drip leg sediment trap.
  • Temperature & pressure relief valves (T&P Valves) that are installed incorrectly. T&P valves serve to monitor and relieve pressure from inside the water heater. These valves should be installed in a downward direction with a discharge pipe directed to the exterior of the house. These valves should never be capped or plugged.
  • Water heaters installed in a location that prevents access for service and maintenance.

3 Warning Signs Your Water Heater May Explode

A Leaking T&P Valve

The number one warning sign that your water heater could explode is a leaky T&P Valve. When too much pressure builds inside the tank the temperature & pressure relief valve can discharge hot water. A leaky valve or a valve that routinely discharges is a tell-tell sign a problem exists. 

This T&P valve will leak due to proper operation if too much pressure exists inside the tank. If you see this valve leaking or routinely discharging water you should immediately have the water heater serviced by a licensed plumber. You may need to lower the temperature setting or replace the T&P valve.

Rotten Egg Smell

If you have a gas water heater and have a rotten egg smell around the outside of the water heater you likely have a gas leak. 

Natural gas and propane have a sulfur or rotten egg type smell. This is done so on purpose so that in the event a gas leak occurs it can easily be detected before an explosion occurs.  The odor you smell is ethyl mercaptan which is added to natural gas and propane to make the gas detectable by smell.

If you suspect your water heater has a gas leak you should immediately turn the gas off to the water heater and call in a licensed plumber to inspect and make any necessary repairs. 

Unlike natural gas and propane gas, carbon monoxide gas is a colorless, odorless gas that is a by-product of the combustion process. This gas is extremely dangerous and can only be detected by specialized equipment. You can’t see it or smell it. Carbon monoxide can cause sickness, debilitating injury, and even death.

Insider’s Tip: Consider investing in an Explosive Gas Detector to install near your gas water heater. The Kidde AC Plug-in Carbon Monoxide and Explosive Gas Detector Alarm provides protection against Natural Gas, Propane Gas, and Carbon Monoxide. These explosive gas detectors are inexpensive and easy to install.

Gurgling, Knocking, or Popping Sounds

Gurgling, knocking, and popping sounds from inside the water heater are a sign that sediment has built up and hardened inside the tank. These sounds are caused by the water becoming trapped under sediment. As the water heats up and expands the hardened sediment moves around inside the water heater. 

One of the causes is when the anode rod, a sacrificial rod located inside the water heater, has been eaten away by acidic sediment inside the tank. Without a line of defense, the harsh sediment begins to attack the internal tank. This, in turn, weakens the internal tank making it more susceptible to an explosion from increases in pressure inside the water heater. 

Smelly Hot Water

Speaking of anode rods, if your hot water smells like “rotten eggs”, the most likely cause is anaerobic bacteria present inside the water heater that reacts with sulfur, magnesium, and aluminum sacrificial anode rods inside the water heater. As the anode rod deteriorates, hydrogen sulfide gas is produced creating a rotten egg smell in the hot water supply.

If your hot water smells bad, the sacrificial anode rod is likely completely eaten away. Once the sacrificial anode rod is completely sacrificed, minerals in hard water begin to attack the inner lining of the water heater.

This creates weak spots in your water heater. These weak spots can rupture under high pressure inside the tank even if it is within the boundaries of the T&P valve or high limit switch.

How to Prevent Your Water Heater from Exploding

maintain water heater

There are several ways that you can prevent your water heater from exploding. The number one line of defense is proper routine maintenance. Let’s explore some of the actions you can take to protect your water heater and property.

Drain & Flush Your Water Heater

Water heaters require routine draining and flushing as part of the water heaters’ routine maintenance. This maintenance is relatively easy to do but is often overlooked by homeowners.

Draining and flushing your water heater removes sediment that has built up inside the internal tank. This sediment needs to be removed to prevent the internal tank from deteriorating.

It is recommended that draining and flushing your water heater should be done on an annual basis. The process is fairly simple and takes about two hours of your time.

For details on water heater maintenance see our step by step article Water Heater Maintenance Tips to 2X Your Tanks Lifespan.

Inspect Your T&P Valve

The temperature and pressure relief valve should be checked a minimum of twice a year. However, most people never do this. Without routine checks, the T&P valve can clog with sediment preventing it to open when needed.

The valve is normally located on the top or top side of the water heater. Make sure the T&P valve is not capped off or impeded in away way. The temperature and pressure relief valve should have a discharge pipe that terminates approximately 6 inches above the drain pan or to the exterior of the house.

If the T&P valve does not have a discharge pipe you should call a plumber to have one installed. The discharge pipe protects you and your family from scalding hot water exiting the T&P valve unexpectedly. Without a discharge pipe to direct the flow of scalding hot water severe burning can occur as water sprays fro the valve uncontrollably.

Before testing the T&P valve be sure you are wearing gloves and a long sleeve shirt to protect your hands and arms from scalding hot water. 

To check the T&P valve, place a bucket under the discharge pipe (if discharges above the drain pan). Lift the lever to open the T&P valve for approximately 5 to 10 seconds. You should hear water exiting through the discharge pipe into the bucket or to the exterior. 

Check Your Anode Rod

The sacrificial anode rod attracts corrosive particles located inside the water heater and acts as a shield of defense to protect the internal tank. The anode rod protects the internal tank from rust which could weaken the water heater which could cause it to explode. 

The anode rod is located inside the water heater should be replaced about once every three years. There are three types of anode rods available.

Aluminum – Aluminum anode rods are best suited for hard water. The aluminum anode rod can withstand harder water better than other types. Aluminum may be a health problem and is not recommended for drinking.

Magnesium – Magnesium anode rods are the most common type of anode rod. They are more suited for areas where water is softer.  Magnesium anode rods don’t last very particularly where hard water is present. Most water heaters come equipped with magnesium anode rods.

Zinc – Zinc anode rods are really zinc-aluminum alloy anode rods. The ratio of zinc to aluminum is very low, about 1:10. Zinc is added is to prevent sulfur smells in the hot water supply. If you have a sulfur/rotten egg smell in your hot water supply, you can switch out the aluminum anode rod for a zinc anode rod to minimalize the smell.

Replacing the anode rod is a relatively easy procedure however if you are unfamiliar with water heaters or working with water heaters it is recommended you call a licensed plumber to do this.

Lower Your Temperature

lower water heater temperature

Electric water heater thermostats are located behind cover panels on the front of the water heater. These thermostats are typically factory set at 125°. 

The same holds true for gas water heaters except the thermostat is located on the control module located on the front of the water heater. Once the pilot is lit, the control knob is turned to the ON setting and the desired temperature.

Some people adjust the settings as high as 140° or higher. Keeping the thermostat on this high setting will reduce the lifespan of your water heater and could cause frequent discharge from the T&P valve. 

It is recommended that you decrease the temperature to 110-120°. This reduces the wear and tear on the water heater and reduces the pressure inside the tank. This setting should still provide ample amounts of hot water.

Expansion Tanks

Expansion tanks are required on many municipal water supply systems now, However, many water heaters existed before the change took place. An expansion tank is a small tank that is installed on open water systems that protect the system from excessive pressure.

Expansion tanks are partially filled with air, which absorbs the shock caused by water hammer and absorbs excess water pressure caused by thermal expansion.

If you do not have an expansion tank on your water heater, you should contact a plumber to see if you need one. For more information see our article Are Water Heater Expansion Tanks Required?

Installation by a Licensed Plumber

One of the most common problems we find is the improper installation of water heaters. It is relatively easy to go to a home store and purchase a new water heater and install it yourself. 

However, most DIY installs we find are done incorrectly. It is recommended that the installation of a new water heater be done by a licensed plumber. This ensures that the installation meets current code requirements that the homeowner may not be aware of.

Gas water heaters should be installed on an 18” stand to protect the ignition source. Gas water heaters inside garages should also have a pipe bollard or approved vehicle barrier installed to prevent a car from hitting the water heater. Most electric to gas water heater conversions lack one or both of these requirements. 

Many local building codes now also require expansion tanks, seismic strapping, and drain pans which were likely not part of the old water heater installation. 

Check for Gas Leaks

If you have a gas or propane water heater, you should routinely check around the water heater for gas leaks. If you detect a rotten egg odor around the water heater you should immediately shut the gas or propane off and contact a licensed plumber. 

As we discussed earlier, natural gas and propane have an ethyl mercaptan additive to make the gas detectable by smell. Installing an explosive gas detector is recommended.

The Kidde AC Plug-in Carbon Monoxide and Explosive Gas Detector Alarm is a great option that is easy to install. This explosive gas detector features:

  • Protection against carbon monoxide and explosive gasses.
  • A loud 85-decibel pulsing alarm will sound to alert you to a potential problem.
  • Displays the level of carbon monoxide the unit is sensing.
  • Test/Reset Button – Tests unit’s electronic circuitry operation and allows you to immediately silence the alarm
  • Three convenient mounting options

Final Thoughts

The risk of a water heater explosion is not something that should go to bed worried about nightly. Armed with some preventative maintenance and knowledge of the warning signs, you can rest easy that your home and family are safe.

Do you need a Licensed Plumber? We can help!
Get a free estimate from top-rated, screened, and licensed plumbers in your area!

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Hubert Miles

I've been conducting home inspections for 17 years. I'm a licensed Home Inspector, Certified Master Inspector (CMI), and FHA 203k Consultant. I started HomeInspectionInsider.com to help people better understand the home inspection process and answer questions about homeownership and home maintenance.

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