Your water heater is usually set to operate at 120 to 130 degrees Fahrenheit. At that temperature, the water is hot enough for your basic needs and to kill all the pathogens in the tank but will not scald.
Hot Water Suddenly Very Hot: Causes and Solutions – A Brief Summary
- Thermostat Misadjustment: One common cause of suddenly very hot water is a thermostat misadjustment on the water heater. The thermostat may have been set to a higher temperature accidentally.
- Sediment Buildup: Over time, sediment can accumulate in the bottom of the water heater tank. This sediment can trap heat and cause the water at the bottom of the tank to become excessively hot.
- Malfunctioning Thermostat: A malfunctioning thermostat can cause erratic heating, resulting in water that becomes extremely hot before the thermostat shuts off the heating element.
- Adjust Thermostat: Check the thermostat setting on your water heater. If it’s set too high, lower it to a safe and comfortable temperature, typically around 120 degrees Fahrenheit (49 degrees Celsius).
- Flush the Tank: To address sediment buildup, perform a tank flushing procedure. Turn off the power to the water heater, connect a hose to the drain valve at the bottom of the tank, and open the valve to drain out the sediment-laden water. Repeat this process as needed.
- Thermostat Replacement: If the thermostat is malfunctioning and causing temperature fluctuations, it may need replacement. Consult a professional technician to diagnose the issue and install a new thermostat.
- Install a Mixing Valve: Consider installing a tempering or mixing valve in the hot water line. This valve allows you to set a safe maximum temperature for the hot water, reducing the risk of scalding while still providing hot water when needed.
- Professional Inspection: If adjusting the thermostat and flushing the tank don’t resolve the issue or if you’re uncomfortable performing these tasks, consult a professional plumber or technician to inspect your water heater. They can identify any underlying problems and perform necessary repairs or replacements.
How Do I know if My Water Heater is Overheating?
The best way to know if your water heater is overheating is by testing the heating element and thermostat for continuity. You cannot tell if there is sediment build up at the bottom of the water heater tank, unless there are popping/knocking noises.
If you suspect that your water heater is overheating, do not attempt to troubleshoot the problem without turning off power to the water heater first. The heating element maybe shorted and therefore passing current through the tank.
Dash to your main house electrical panel and look for the breaker labeled “Water Heater” or with the initials “WH” on it. Flip it to the off position.
After turning off the power to the water heater, it is time to troubleshoot it. For this job you will need a multimeter, a Philips and a flathead screwdriver.
Now here is how to fix a water heater when the water is suddenly too hot:
1. Test the Heating Element
An electric water heater will most likely have 2 heating elements and thermostats. The upper and lower heating elements are concealed using a cover plate in the 2 access panels.
- Use a screwdriver to remove the upper access panel cover plate.
- With the plate out, you will see a small piece of insulation. Remove it as well.
- Pull out the plastic cover. There will be a piece of plastic covering the thermostat and heating element by snapping on them. Pull it out too.
You can now see the thermostat, reset button, temperature adjustment dial and heating element.
The thermostat is the piece with many screws and wires connected to it while the heating element is at the bottom with only 2 screws and 2 wires connected to it.
A water heater reset button is the little button on the thermostat which in most cases is usually red in color. It is also known as a emergency cut off switch or high temperature limit switch.
The function of the reset button is to turn off power to the water heater if the thermostat fails to turn off the heating element. It does so by tripping when the water temperature reaches and exceeds 1800 F.
Usually, when your water becomes suddenly very hot, it is followed by lukewarm water and later no hot water. This happens when the reset button trips.
To reset this button you will only need to press it till you hear it click.
If however the reset button is faulty as well, the thermostat will remain stuck in the on position. You may notice a leak in your water heater temperature and pressure relief valve unless it is blocked and no longer working.
A broken heating element may make contact with metals inside the water heater creating a short circuit. Current will therefore flow from the element to the metal, causing it to continuously heat the water.
Here is how to test a water heater element using a multimeter:
- Using a screwdriver, loosen the 2 screws on the water heater and pull out the wires.
- Set your multimeter dial to the least ohms of resistance setting.
- If you have an analogue multimeter, pinch the 2 probes together and move the needle to zero. With a digital multimeter, move the dial to the tone settings if you have that option.
- Put one probe on one of the water heater terminals (screw) and the other on the water heater tank body.
- Check the reading on your multimeter.
If there is an ohms reading on your multimeter, there is electrical continuity between the heating element and the tank. The heating element will need to be replaced.
After checking the upper heating element, remove the lower access panel plate and test the lower element as well.
I have written a detailed post on how to replace a water heater element. Read it here.
2. Test the Thermostat
If the heating element is not the problem, you most likely have a bad thermostat. When the thermostat is stuck in the on position, it will keep current flowing to the heating element even after the water is sufficiently heated.
Whenever I test the heating element and it looks ok, I usually replace both thermostats. You can as well buy a complete kit where you will replace both the heating elements and the thermostats.
Replacing the heating element also gives you the opportunity to flush out sediment from the water heater.
While at it, check the set water temperature on the thermostat temperature adjustment dial. If the temperature is set too high, use a flathead screwdriver to adjust it to 1200 F.
I have written a guide on how to test and replace an electric water heater thermostat. Read it here.
3. Flush out Sediment from the Tank
If you live in an area with hard water, dissolved minerals and especially calcium will settle at the bottom of the water heater forming sediment. This sediment will not only reduce your water heater’s volume, but it will also impact its heating efficiency.
If you are using a gas water heater which is heats water from the bottom, it will take longer for the heat to be transferred to the water through the layers of sediment. Before your water heater senses the water temperature has exceeded the set level, the water will already be scalding hot.
In electric water heaters, heating elements will also be coated with minerals deposits, forcing them to overheat in order to sufficiently heat the water. You may also here popping noises form the water heater as well.
A good way to fix this problem is flushing out sediments from the water heater. You just need to turn off the power or gas supply to the water heater then shut off the cold water valve.
After that, connect a garden hose on the drain valve bib and drain out the tank. While refilling the tank, have one hot water faucet open to prevent air building up in the tank.
I have written a complete guide on how to flush out sediments from a water heater. Read it here.
If you have not flushed your water heater in years, doing it now will make almost no difference. You can however attempt to vacuum the minerals through the water heater element opening as shown in this video.
4. Check the TPR Valve
The water heater temperature and pressure relief valve also known as the T&P or TPR valve is the valve at the top of the tank with a vertical discharge tube connected to it.
The function of a TPR valve is to discharge little amounts of water from the tank when the conditions are too high, to prevent it from bursting. TPR valves will usually open and discharge water at 150 PSI (pounds per square inch) or 2100 F.
To check if your TPR valve is working properly, place a bucket under the discharge tube and lift off the lever on the valve. If you see some water being discharged on the bucket, the valve is good.
On the hand, if no water comes out of the discharge tube then the valve is blocked. A blocked temperature and pressure relief valve is quite risky since the tank may explode and will therefore need a replacement.
I have also written a guide on how to replace a TPR valve. Read it here.
5. Call a Plumber
If you have tried troubleshooting you water heater with no success or you are not confident or able to do it, pick up the phone and call a professional plumber to solve the problem for you.
A plumber will have seen such a scenario plenty of times and will therefore know exactly where to look and what to do.