Most electric water heaters have two thermostats, one behind the upper access panel and one behind the lower, and both need to be set correctly for consistent hot water. The job takes about 15 minutes, requires only a couple of screwdrivers, and can save meaningful money on your energy bill. Here’s exactly how to do it safely.
What You’ll Need
The tool list is short: a Phillips screwdriver or ¼-inch nut driver to remove the access panels, a flathead screwdriver to turn the thermostat dials, and an instant-read thermometer to verify the temperature at a faucet afterward. A non-contact voltage tester is worth having if you own one, though it’s not strictly required as long as you confirm the breaker is off before touching anything.
Turn Off the Power First
Go to your electrical panel and flip the breaker labeled for your water heater. Many electric water heaters are wired to two circuit breakers on a 240-volt supply. Both breakers must be shut off. If your heater has a dedicated power switch on or near the unit, turn that off too. Do not skip this step. You’ll be working inches from live wiring, and the risk of shock is real.
Access the Thermostats
Electric water heaters typically have two metal access panels on the front of the tank, one near the top and one near the bottom. Use your Phillips screwdriver or nut driver to remove the screws holding each panel in place. Behind each panel you’ll find a layer of insulation (usually fiberglass or foam) covering the thermostat. Pull the insulation out of the way or fold it aside. Underneath that, there’s a plastic safety cover that either pops off or hinges upward. Remove or lift it to reveal the thermostat dial.
Choose the Right Temperature
For most households, 120°F is the sweet spot. It’s hot enough for comfortable showers and general cleaning while keeping scald risk and energy costs low. At 120°F, the Department of Energy notes a very slight risk of Legionella bacteria growth, but this temperature is still considered safe for the majority of the population.
You may want to go higher in a few situations. If your dishwasher doesn’t have a built-in booster heater, it may need water between 130°F and 140°F for proper sanitizing. If anyone in your household has a suppressed immune system or chronic respiratory disease, 140°F helps kill Legionella more reliably. The EPA notes that Legionella thrives between 80°F and 120°F, and setting the thermostat at or above 140°F keeps temperatures high enough throughout your plumbing to prevent growth.
The tradeoff with higher temperatures is burn risk. According to the Consumer Product Safety Commission, 140°F water causes third-degree burns in just six seconds. At 150°F, it takes only two seconds. Even at 120°F, prolonged contact of five minutes can cause serious burns. If you have young children or elderly family members, keeping the setting at 120°F is the safer choice.
Set Both Thermostats
Here’s the part most people get wrong: both thermostats need to be adjusted, not just one. Using a flathead screwdriver, turn the dial on the upper thermostat to your desired temperature. Then move to the lower thermostat and set it to the same temperature, or just slightly higher than the upper setting. Setting the lower thermostat a touch higher ensures more even heating throughout the tank, since the upper thermostat controls the top heating element and the lower handles the bottom.
The dials on most electric water heaters have notches or labeled temperature markings. Some only have vague ranges like “warm” to “hot” without specific degree markings. If yours lacks numbers, you’ll need to test and adjust in small increments until you hit your target temperature at the faucet.
Reassemble and Wait
Once both thermostats are set, replace the plastic safety covers, push the insulation back into position, and reattach the metal access panels with their screws. Then flip the circuit breaker(s) back on. The water heater needs time to reach its new temperature setting, so give it at least one to two hours before testing.
Verify the Temperature at a Faucet
After the heater has had time to recover, pick a faucet close to the water heater for the most accurate reading. Turn on only the hot water and let it run for a full three minutes to clear any cooled water sitting in the pipes. Fill a cup or bowl with the running hot water and check it with your instant-read thermometer. If the reading is off from your target, go back to the thermostats and nudge them up or down, then wait and retest. It may take a couple of rounds to dial it in, especially on heaters with unmarked dials.
Signs Your Thermostat May Need Replacing
If you’ve adjusted both thermostats but your water temperature is still inconsistent, scalding one moment and lukewarm the next, the thermostat itself may be failing. A complete lack of hot water after adjustment points to a thermostat or heating element that has failed entirely. Unusual humming or buzzing from the tank can also indicate the heater is cycling erratically rather than heating in a normal pattern.
Most water heaters last between 8 and 12 years. If your unit is in that age range and simple thermostat adjustments aren’t solving the problem, the issue is likely beyond a DIY fix. A failing thermostat or element on an aging tank is often the signal that replacement of the whole unit makes more sense than continued repairs.