5 Reasons Why Your Water Heater is Overheating: Here's What to Do to Fix It

Hot water tap and how to save energyImage by Reto Gerber from Pixabay

We are all happy to turn on the hot water in the morning as we prepare to get ready for work. This morning, however, is different. As you wait a few seconds for the hot water to come through, you get a shock. It's steaming hot and spluttering out of the tap like it's boiling. You are instantly wide awake and have the common sense not to touch it. You turn off the faucet and head to the basement to check out the cause.

Why is my water heater overheating?

What things should you check in these circumstances?

5 Possible causes and how to repair them

Here's a list of five possible causes of why hot water is getting too hot and what you can do to fix the problem and avoid similar issues in the future.

  1. Thermostat setting
  2. The reset button has popped out
  3. Faulty thermostat
  4. Faulty heater element
  5. Faulty temperature & pressure (t&p) relief valve

Thermostat setting

I know it's so obvious, but it happens all the time. The incorrect setting on the thermostat is a widespread reason for your water temperature to be too high. In most water heaters, such as gas type or tankless the thermostat is easy to access and change the settings.

In other units, such as electric type, they are deliberately more challenging to change and need you to remove an access panel/insulation and the blade of a screwdriver to move the setting up or down. It's unlikely, but it's the easiest thing to check first.

If your heater has a digital thermostat, it can be attractive to kids to fiddle with; they love anything digital. It's when you discover the water temperature is scalding; you go check.

It's an easy fix. Many state laws set a maximum of 120 F for water heaters. However, they have no control over the purchaser who changes it for hotter water once they install it in their home.

As per HVAC equipment manufacturers, water temperatures above 125 F can cause severe burns, even death from scalding.

Recommended settings

The recommended setting is there because it is a safe level for hot water. However, you may choose to reduce it, especially if you have older people living in your home or children who don't think before putting their hands into the water flow as soon as it's flowing and suffering burns.

In addition to safety, if you reduce the temperature by only 100 F, you will save money; as much as 3 and 5 percent of your annual water heating bill. Now that's worth doing, isn't it?

If that has fixed your problem, that's excellent. However, make sure you are still careful. It will take your hot water tank full of scalding water a long time to drop back to a safe level. Make sure you warn everyone in the house about the possible danger until it's cooler. 

If that wasn't the answer, what do you check next?

To determine the proper water temperature for your home, check out the table below, showing time/temperature relationships in scalds:

Water temperature Time to produce a serious burn
120 F More than 5 minutes
125 F 1 1/2 to 2 minutes
130 F About 30 seconds
135 F About 10 seconds
140 F Less than 5 seconds
145 F Less than 3 seconds
150 F About 11/2 seconds
155 F About 1 second

The reset button has popped out

Another simple thing to check is the reset button (known as a high-limit switch) on your thermostat. It's fitted as prevention from overheating. It will trigger if the water in the tank exceeds 180 F, where there is a clear danger from scalding. It automatically shuts off the power or gas supply to the water heater to prevent rising temperatures. The mechanism protects you, your home, and the water heater.

A faulty thermostat can trigger the reset button. If it's defective, it won't send a command to the heater elements to switch off when they reach the desired temperature. The heaters will continue to heat, and the reset button is the next line of defense. If it has tripped, there could be a problem that needs further investigation. Push it back in to reset the system. If it pops again, you need to have it checked by a professional plumber.

Three other reasons why the reset triggers

A defective thermostat is often why the reset button has triggered; however, there are other causes:

Faulty element. If the thermostat is operational, it will close down the element correctly. On the other hand, if there's a damaged circuit in a heater, it could mean it resumes working to continue to heat the water.

Loose connections. If you have a loose connection in the heater, it can cause an increase in heat, which could trigger the reset switch.

Faulty switch. The switch itself may be faulty and cutting out when it shouldn't, which will cause it to cut out when everything else is good.

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Faulty thermostat

Faulty thermostat?

They can and do fail. If you have a modern thermostat, it may run from batteries, which need changing from time to time. Check them first. They work in relatively inhospitable conditions, and they often simply stop working and need to be replaced. If you have a meter, you can check to see if it's operational, but of course, you must shut off the mains power to the heater before you do anything. Otherwise, call a professional plumber.

If you find your thermostat is at the correct setting and the water has almost boiled, the thermostat may have failed. Remember, there are two thermostats in electric water tank heaters, one near the top and one near the base, which works in tandem. When the thermostat fails to work correctly, the heating elements continue to heat the water, increasing its temperature to an unsafe level.

In gas models, the thermostat is part of the gas control valve assembly, and it is installed near the bottom of the unit. If it fails, the whole assembly has to be replaced.

Faulty heater element  

In electric heaters, the elements attract minerals from your water supply, which calcify on parts of your heater, including the heating elements. If this layer of calcification thickens and builds up without regular cleaning, it can cause the elements to overheat in an attempt to heat the water to the required temperature. They lose efficiency because they have a mineral coating.

With a gas-fired heater, the base of the heater can become covered in a thick layer of sediment and sludge, which makes it harder to heat the water to the correct level. This can cause the water to overheat. The gas struggles to heat the water efficiently.

Tankless heaters that don't have a reservoir are still at risk from mineral build-up. It is especially prevalent in hard water areas. It can reduce the unit's efficiency and pass minerals through the system to faucets and shower valves, resulting in low flow. The mineral build-up can damage the inside of the unit and block relief valves, increasing the risk of damage to the unit and your home.

Faulty temperature & pressure (T&P) relief valve

If there's water in the drain tray or floor around your heater, with no apparent leak, it is likely that your temperature and pressure (T&P) relief valve is faulty and leaking water. These valves are designed to open and release high pressure above 150 psi for safety reasons and if the water temperature exceeds 210 F.

Checking your T&P valves regularly is essential. It only takes a few seconds. Open them up and flush water through to clear sediment that may have built up inside the valve. Once it's cleaned, it should snap shut tightly again and be a watertight seal. If it jams open, you could have a serious flood in itself, but if it sticks closed, there is a danger of explosion and risk to your family and home. Check the T&P relief valve regularly, and if it appears clogged up, it's essential to have it professionally checked and replaced if necessary.

If you hear sounds like boiling from your water heater, it can indicate the water inside is too hot. It would be best if you shut it down to prevent serious accidents, including explosion.

Before you begin

Before you begin any work on your water heater, turn it off on the circuit breaker box and gas supply. Safety first.

Inspect the main electrical wires that are not extremely hot, melted, or have burnt areas.

Testing the heating element will show if it is shorting or not. A shorted element is one of the reasons for overheating.

In gas water heaters, the gas valve controls the temperature of hot water, and if your manual adjustment does not correctly set the temperature, you have to call a technician to replace it.


Overheating in your water heater is dangerous. You may only discover it when someone turns on the faucet and gets scalded. By then, it's too late. It's especially hazardous in showers and with the elderly, infirm, and of course, your children.

The takeaway from this piece is maintenance. Simple, low-tech regular upkeep of your water heater system is essential. It is often completely ignored until something goes wrong, like overheating, when the neglect comes back to bite, always when you least need it.

A few simple checks are all that you need to do regularly, and if you don't feel you are up to it, that's perfectly fine safeguard your family and call a professional plumber who will service and check it for you to guarantee a problem-free life.

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