Is your water heater suddenly producing scalding hot water that could burn you? Having an extremely hot water heater can be dangerous, not to mention energy inefficient. As a retired plumber with decades of experience, I’ve seen all the reasons why home water heaters can start overheating and pumping out dangerously hot water.
In this article, I’ll walk you through the top 10 most common causes behind a hot water heater that’s getting way too hot. I’ll also explain how to troubleshoot and fix the problem, so you can get back to enjoying safe hot water temperatures again.
1. Faulty Thermostat
The thermostat controls the temperature of the water inside your heater. It’s supposed to keep the water at a safe and comfortable temperature around 120°F. If the thermostat malfunctions, it could stop regulating the temperature properly. This allows the water to keep heating higher and higher.
You’ll want to test and make sure your water heater’s thermostat is still accurately measuring water temperature. Turn the temperature down, then after a while, run a small amount of hot water into a cup and use a thermometer to test the temperature. If it’s much higher than the thermostat setting, the thermostat needs to be replaced.
2. Worn Out Heating Element
Electric water heaters have one or two heating elements that warm up the water. As they age, sediment and mineral buildup causes them to slowly lose efficiency. An old heating element may stay on too long trying to heat the water, causing overheating.
To fix this, the electric heating element needs to be inspected and replaced if it’s worn out. Also flush the water heater to remove built up scale on the element.
3. High Temperature Setting
Sometimes the cause of an overheating water heater is simply that the temperature setting is dialed up too high. Electric water heaters usually have a thermostat dial that sets the desired hot water temperature. If yours is set too high, check the thermostat and lower the temperature to a safer and more efficient level around 120°F.
4. Sediment Buildup
Over years of heating water, scale and sediment accumulates at the bottom of the water heater tank. This buildup insulates the water from the heating element. So the heating element has to work much harder to warm the water, potentially leading to overheating.
To fix this, flush out the tank to clear built up sediment. Draining a few gallons from the tank’s drain valve weekly can help prevent excessive sediment buildup.
5. Water Pressure Too High
If your home water pressure is too high, the heating elements in an electric water heater have trouble properly warming the water before it exits the tank. This can cause the elements to rapidly cycle on and off trying to heat the water, potentially leading to overheating.
Inspect your water pressure to see if it’s higher than 80 psi. If so, install a pressure reducing valve to maintain a safe pressure.
6. Faulty Gas Control Valve
Gas water heaters use a gas control valve to regulate gas flow and the burner flame. If this gas valve sticks open, gas will continue flowing to the burner and overheat the water. The valve must be repaired or replaced to resolve this overheating risk.
7. Undersized Water Heater
Using too small of a water heater for your household’s needs can cause it to overwork itself trying to keep up with demand. This leads to the unit running excessively, potentially overheating the limited tank capacity.
If your water runs out quickly and you have an older unit, upgrading to a larger water heater may provide a solution. Properly sizing your new unit for your home’s needs can prevent overheating.
8. Damaged Pressure Relief Valve
All water heaters have a pressure relief valve as a safety device. If the tank pressure gets dangerously high, this valve will open to release excess heat and pressure. But if the valve is defective and fails to open, pressure can continue building up causing overheating.
Inspect the pressure relief valve and replace it if it’s broken or blocked. This provides a backup safety mechanism to prevent the tank from over pressurizing.
9. Hard Water Causing Scale Buildup
If you have hard water, calcium and magnesium in the water can leave behind scale deposits on the water heater’s interior surface. This mineral buildup acts as insulation that leads to overheating by interfering with heat transfer.
To remove mineral deposits, flush the tank and install a water softener if your water supply is very hard. Preventing scale buildup helps the tank run efficiently.
10. Short Cycling On and Off
Frequent short cycling (turning on and off repeatedly) can lead to accelerated wear and failure of components like thermostats, valves, and heating elements. This malfunctioning equipment could then lead to overheating.
What causes short cycling? Things like a leaking hot water tap, an undersized heater, or a defective thermostat. Correct the source of the short cycling to stop unnecessary heating element wear and overheating.
Know the Signs Your Water Heater is Overheating
How can you tell if your water heater is dangerously overheating? Here are some key signs:
- Hot water burns or scalds your skin
- Water at faucets and shower heads is too hot to use
- The water heater makes sizzling, popping, or rumbling noises
- You see steam or condensation coming from the tank
- The water heater outer metal surface feels hot to the touch
- You have rust-colored water coming from faucets
- There is a burning or smoke odor coming from the unit
If you notice any of these warning signs, your water heater may be overheating and should be inspected immediately.
Prevent Water Heater Overheating
Want to avoid overheating issues in the future? Here are some tips:
- Drain the tank periodically to remove sediment
- Have your water heater serviced once a year
- Use a water softener if you have hard water
- Keep the thermostat at 120°F or less
- Install a pressure reducing valve if over 80 psi
- Upgrade to a larger heater if your home needs more capacity
A well maintained water heater should provide hot water at a safe temperature for many years. But if problems develop, act quickly to correct overheating and prevent potential damage or injuries.
I hope this overview gives you a better understanding of why your hot water may be scalding hot all of a sudden. As a retired plumber, I’ve seen these common issues many times. Catching and fixing overheating water heaters quickly is important for your safety. If in doubt, call a professional plumber to inspect your system and get the problem resolved. Stay safe and keep those hot water temperatures in a safe range.
