women turning on bath tub tap

5 Reasons Why Your Water Heater is Scalding Hot

“Ouch, that’s hot!” Sounds familiar? If the water from your water heater is scalding hot, you’ve got three problems on your hands.

Firstly, there’s the risk of serious burns from extremely hot water from taps and fixtures in your home. This is a major concern, especially if you have the young or the old using your water.

Second, you have a malfunctioning water heater to worry about.

And finally, you can expect a big energy bill just around the corner!

If the hot water from your water heater is too hot, it could be due to a faulty thermostat, mineral build-up, blocked pressure relief valve, your system’s heating element or even the tempering valve.

How hot is too hot for hot water heaters?

Most water heater thermostats are set somewhere between 60 and 70°C. But did you know that 70°C water will burn adult skin in just 1 second and a child’s skin in just 0.5 seconds according to Australian Building Codes Board?

Adults and children can enjoy 50°C water for 5 minutes before risk of scalds. At 45°C, that time goes up to 6 hours! If 60-70°C water is too hot and will cause burns, then why don’t we set the thermostat to 50°C?

When storing water in a water tank to be heated, you run the risk of bacteria growing inside. Setting the thermostat at 60-70°C means you minimise this risk.

That’s why it’s a regulation for Australian homes to have tempering valves installed for sanitary fixtures such as your shower and bathroom tap. These control the temperature allowed to come out of these fixtures.

At most you’ll have 50°C, which is safe for up to 5 minutes for both adults and young children. Mix in some cold water and you’re all good to have those long showers we all love.

1. Thermostat is set too high or is broken

plumber adjusting water heater thermostat

Both electric and gas water heaters have a thermostat, or a temperature setting to heat the water to. If you have really hot water coming from your hot water system, it’s best to start off checking this.

The thermostat helps to regulate the temperature of your hot water heater. The temperature it senses controls whether or not the system’s heating elements are off or on.

Check your thermostat and see what temperature it is set to. If this is too high, this is what is causing your water heater to produce scalding hot water.

Alternatively, your water heater thermostat might simply be broken. This could be a miscalibrated thermostat, meaning the temperature it reads is consistently lower than what it actually is. Or maybe the safety trigger is broken and your water is constantly being heated.

Regardless, a thermostat replacement is no DIY job – you will need to contact a professional plumber to make sure the job is done right.

2. Mineral build-up

Our water contains a range of minerals which aren’t filtered out during water treatment processes. Water with an especially high concentration of minerals is considered hard water.

An excessive build-up of minerals in your hot water heater could be a cause of a high water temperature. These minerals eventually settle at the bottom of your water heater and form a hard layer or sediment.

This layer will mean more energy is required for water heating. It can also cause overheating and can heat your water to much higher temperatures than it is set to. On top of unexpectedly hot water, this will also decrease your water heater’s lifespan.

3. Pressure relief valve is blocked

5 Reasons Why Your Water Heater is Scalding Hot

The pressure relief valve is a very important component of a hot water system. Water inside the tank is heated and steam is generated. The pressure relief valve helps to release this steam and regulate the tank’s pressure.

If the pressure relief valve is blocked, pressure inside the tank will increase, in effect overheating the water. This could be a cause of your hot water suddenly becoming too hot. Worst case scenario, your water heater might explode!

With the risk of explosion, this is certainly a problem to call a plumber for. You’ll need an emergency plumber with a quick turnaround time if your pressure relief valve is blocked.

4. Malfunctioning heating element

Electric water heaters contain one or two heating elements inside the tank to heat the water. If you suddenly have scalding hot water from taps in your home, this could be a sign that a heating element is stuck on.

It is often the lower element that sticks first due to the sediment layer on the bottom. This means it is constantly heating, causing the water to overheat.

Just like the problems above, replacing a heating element could be disastrous for an amateur. Mixing electrical heating elements and water should only be done by a professional plumber.

5. Your tempering valve is faulty, or you don’t have one!

Your hot water system’s tempering valve limits your water’s maximum temperature to 50°C for sanitary fixtures. If this valve is faulty, your water could be coming out much hotter than this maximum, risking serious scald burns.

If you have an older water heater, you might not even have a tempering valve to begin with! Tempering valves are now required for new water heater installations.

While regulations vary slightly between states, a general rule of thumb is that if you’re having a new water heater installed, even if it’s like-for-like, you need a tempering valve.

No matter what reason your water heater is scalding hot, Metropolitan can help with our 24/7 availability and service within an hour*. We have all your plumbing needs sorted with our experienced emergency plumbers.


Published: 4 Feb, 2021

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