Can A Water Heater Explode?

can water heater explode

A hot water heater is a household appliance that is found in most if not all homes as at now. Its main purpose is to heat the water that comes down the shower, to do the dishes or laundry. In previous times you would turn on the heater a few minutes in advance before you jumped into the shower, but with recent advancement nowadays it is instantaneous with the flick of a switch.

As they are widely accepted and found throughout many of our homes, we should be well aware of the risk they pose to our personal safety. The answer to this question if the heater can explode is yes. But for a better understanding of how this catastrophic occurrence can unfold, you should first familiarise yourself with how a water heater operates.

can water heater explode

How a Water Heater Functions

There are two main types of water heaters governed by the method they heat the water. Mostly electricity and gas burners exist. For the gas burner; it is a heavily insulated metal tank with the gas burner right beneath it. The thermostat regulates the amount of gas that burns which effectively alters the temperature of the water. As the gas burner heats the water tank the exhaust gases produced need to escape out through the chimney and vent shaft which also helps in raising the water temperature as exhaust gases are considerably hot.

Cold water is let in the boiler through The Dip tube which extends from the top of the boiler to near the base. The hot water to be used exits the boiler through the heat-out pipe to the various outlet taps that require hot water. As the water temperature rises, it expands and the steam inside the boiler increases the internal pressure. When these stresses become overwhelming the temperature and pressure relief valve open to let out this excess build-up.

Failure to do this could lead to pressure and temperature that the boiler cannot handle and consequently lead to an explosion. This valve is the main reason for failure and many water boilers exploding. The water that goes into the boiler is not entirely soft and contains minerals. These minerals at high temperatures tend to sediment and sink to the bottom of the tank and should be drained through the drain valve close to twice a year. The anode rod is located in the boiler and its main function is to sacrificially protect the inside metallic parts of the boiler from corrosion.

The electric water heater works more or less in the same way, the only difference is that instead of a gas burner It uses electric coils under power supply to generate heat that warms the water.

What Could Cause a Water Heater Explosion?

The home water heater is a safe appliance and has been designed to work under conditions it can handle. When these conditions are no longer met and exceeded, it becomes potentially life-threatening.

1st scenario

The set temperature that a boiler operates on is approximately 120 degrees Fahrenheit ( but may differ). When this temperature is exceeded through a faulty thermostat or due to excessive sediment build-up the expanding water exerts an outside force on the boiler. This force normally escapes through the temperature and pressure relief valve but if this is faulty as well and does not open then think of it as a balloon that is continually inflated. It reaches a point it can handle the stresses no more and explodes violently.

2nd scenario

When the water is converted to steam, gas occupies more volume than the liquid state and this introduces a lot of pressure in the enclosed vessel. Without letting off the excessive pressure, it exceeds the mechanical strength of the material used to make the heater, and just like the previous scenario a buildup of pressure with no release leads to a catastrophic explosion.

3rd scenario

Water is very corrosive in nature, especially towards metal. Saltwater in particular speeds up the corrosion process. If hot water is continually used then make sure you relieve the boiler of sediments and constantly check on the anode rod. Since this rod is usually sacrificial I.e it corrodes leaving the tank intact. It may be completely eaten away and Rust starts to act on the tank itself. Rust may manifest and diminish the material strength of the boiler. This is very dangerous as now even the normal operating conditions could be risky as the material can no longer handle it making it blow up or breaking away leading to leaks. This could pour out scalding hot water harming those around.

4th scenario

This is specific to the gas water heater. Send flammable gas is used as the fuel you should always make sure all fields and piping is airtight to prevent any gas leaks. When flammable gas seeps through and noticed and the flame is ignited say from a pilot burner or any lighter then they will most definitely be a gas explosion. But this is not directly the boiler exploding it is a possibility and so you should always be keen even to fit gas sensors just to be extra careful.

The explosion from a water heater is without a doubt fatal and can cause extensive structural damage to your home. You’d be lucky if you survive and so always check the p&t valve to make sure it is free from sediment and it functions right. Drain the tank to get rid of sediments and always stay clean if using a gas burner. Always keep within the operating limits of the heater to be on the safe side.

Signs That Shows a Heater is About to Blow

●Crackling noise when operating.

This comes about as a result of the sedimentation of the minerals contained within the hard water. As the water tries to escape this layer it produces this noise. With sediment build-up, it accumulates and takes up space within the boiler, and when heating the pressure within could rise above the allowable pressure causing a hazard. Also, sediments can diminish the mechanical strength and consequently compromise the structural integrity of the heater. Make sure to drain the sediment occasionally to avoid accumulation.

●T&P valve leakage

This is more often the source of the problem and it is critical to check that this valve operates as intended. Ie opens and closes at the right temperature and pressure. If not a specialist should come and inspect it and replace it if need be.

●Tank leakage

When the tank itself starts leaking it is a sign that the tank has been eaten away from the inside and becomes a safety risk. It means it can no longer take the high pressure and would be wise to replace it before anything bad happens.

●Water that looks rusty

This may be because the anode rod is done for and can no longer protect the insides of the boiler. This could be an indication that the internal parts have succumbed to corrosion and it is clear that replacing and maintenance should be done.

●Rotten egg smell

This is the smell of unburnt hydrocarbon gases and if noticed a gas leak is imminent. Be careful not to ignite a spark or flame when you notice the smell as it could lead to an explosion. Call a relevant specialist to come and tighten all fitting that the gas could be escaping from to avoid casualties.


Though a water boiler explosion is not common as such, it has occurred a couple of times in the past. If we are to learn from our mistakes then we should always keep a close eye on this appliance. You should always call a certified professional to do your maintenance once or twice a year just to make sure that everything runs as expected. You should; flush sediment, change the anode rod, check the thermostat, check the pressure relief valve and check for gas leaks ever so constantly.


David: Penn State-educated Mechanical Engineer and Business-savvy Fluid Dynamics Specialist. Balances family plumbing business support with a thriving engineering career at a top, undisclosed company. (they want it that way) I help Will with plumbing and HVAC needs on his Real Estate.

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