Can a hot water system explode?

Fast read

Hot water system explosions are very rare nowaday but can be very dangerous, with the risk of causing serious injuries. However, there are several modern safety mechanisms inbuilt in your hot water tank to prevent such accidents.

The most common cause of issues in hot water systems is a faulty pressure relief valve, which regulates the pressure within the hot water tank. If the valve leaks, it is a sign that the valve is stuck or that the components cannot handle the internal pressure and needs professional attention. Sediment buildup in the tank and DIY jobs, especially on the thermometer can also cause problems that may lead to a hot water system rupture.

To avoid these issues, routine maintenance is important, and any signs of malfunction such as failing pressure relief valve, abnormal noises, brown water indicating internal decay should be checked by a professional plumber.

Is there a risk of my hot water system exploding?

While a hot water system can explode, it is very rare, but when they do occur, they can be dangerous. The force released can break through walls, with scalding water sometimes causing severe injuries. Nevertheless, several modern-day safety mechanisms prevent serious damage, so that this type of accident is literally impossible. Therefore, no need to remain in your home, constantly worrying about the risk of potentially serious injury at any moment.

While it is very rare nowadays, there are several reasons your hot water system could explode. 

What could be the causes of your hot water system exploding? 

Faulty pressure relief valve

The most common cause of issues of pressure built up in a hot water system is a blocked pressure relief valve. As the name suggests, this valve regulates pressure within the hot water tank. As a result of the natural heating process and the creation of vapours/steam, pressure in the tank builds up. Should the pressure inside the tank become too high, the pressure relief valve will release a certain amount of boiling water. But if this valve is broken, the pressure can build up, potentially leading to an explosion.

If you notice that your pressure relief valve leaks all the time or very frequently, it is most likely a sign that the part has become stuck or become faulty. It is also advisable to test and operate the pressure relief valve every 6 months just to check that it works. It is a simple test that can be performed by anyone. 

How to test if the valve is working properly?

Go to your hot water tank; on the side, there is a copper pipe that looks like a spout, as it is open at the end. It usually finishes  10  to 20 cm above the ground if outside. Up the top, where the pipe leaves the tank, is the location of the pressure relief valve. On top of it is a little hook, which allows you to test the valve. Push the hook/handle backwards till you hear water leaving the tank and spilling onto the ground. Be careful the water will be hot. 

Then let the handle go, and the valve should snap back into the close position. If the water continues to run after you let go, the valve is faulty, and you to to get it replaced. A faulty pressure relief valve can waste a lot of water over time and becomes expensive in regard to electricity costs and wasted water.  So if you notice this valve leaking, it is recommended that you get it professionally looked at.

hot water tank on the road
Electric hot water tanks usually have a lifespan of 10-plus years

Sediment build-up

Another cause for concern is sediment build-up in your hot water tank. Failure to maintain your tank correctly can result in sand and mud entering through the water inlet, leading to sediment buildup. Without regular tank flushing through usage, minerals in the water can cause sediment to accumulate at the tank’s bottom. This becomes a form of insulation, forming a crusty layer at the bottom of the tank that water could become trapped within. This could impact the ability of the tank to heat water. The presence of a popping sound typically signals this issue: sediment accumulating at the tank bottom, posing a risk of overheating. Furthermore, sediment can cause problems with the pressure relief valve by blocking the valve itself, potentially causing an increase in pressure in the tank. 

DIY jobs

DIY jobs are another problem that can cause a hot water system to explode. While some Australians might believe that a standard hot water tank issue doesn’t justify contacting their plumber, many homeowners could face surprise gas leaks or malfunctioning pressure valves without realising it. It’s never advisable to replace this valve or handle a tank leak without professional assistance. Moreover, if you work on the system yourself, you void the warranty for your tank system.

Faulty thermostat

Each electric hot water system has an inbuilt thermostat, usually at the bottom of the tank, behind a square inspection cover. While in older electric hot water systems, one could set the temperature close to the boiling point, modern hot water tanks, even if in the hottest position, will only heat the water to about 65 degrees Celsius in order to avoid scalding, via the hot water outlet, especially in children. A malfunctioning thermostat that can’t measure water temperature accurately might overheat the water, leading to increased pressure. If the pressure relief valve is blocked as well, the tank could theoretically explode.

Corrosion and rust in the tank due to age

If the tank or its parts are corroded, usually on the bottom, where sediments can build up, they can weaken the tunk structure and fail under pressure. This will, over time, lead to a rupture and is the most common reason for a tank failure, usually around years 8 to 12. If your water heater is old and showing signs of rust or corrosion via brown water leaving the tank and coming through the tap, it might be time to speak to a professional about replacing it.

burst water pipe
Water pressure and temperature together create a force which can cause a rupture of the equipment

High water pressure

 High water pressure entering the tank increases the overall pressure inside the tank. Without a properly functioning pressure valve to relieve this pressure, there is a risk of an explosion. In modern water supply, it is highly unlikely your water pressure could reach a point where it could cause such damage. 

How can I avoid a potential risk? 

When it comes to preventing a hot water heater explosion, routine maintenance is the greatest defence. Your local plumber will inspect the pressure relief valve and venting system and ensure the timely replacement of all components, including any sacrificial anodes.

It is also worth regularly checking on the system yourself between visits from the plumber. As mentioned above, you can self-test the pressure relief valve, check if your hot water suddenly has become much hotter, and monitor for signs of rust or corrosion.

If your water supply is very mineral or sediment-heavy, a plumber could drain the tank every 4-5 years to remove sediment. You can also ensure via the thermostat setting that you keep the temperature of your water heater set to between 49-51 degrees Celsius. Such a temperature will help to reduce the risk of higher temperatures causing the water tank to expand and reduce the risk of pressure build-up. Lowering the tank temperature slightly has one drawback: it reduces your overall hot water capacity, potentially causing the system to run out of hot water faster, especially if three family members take showers one after the other.

Meanwhile, keep an eye on your tank’s functionality and consistency

Important indicators that something is wrong are:

  • A pressure relief valve that is blocked or run constantly
  • Noises from the tank that are out of the ordinary
  • Decay, such as rust, leaks or cracks
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