Most water heaters can be adjusted in just a few minutes, though the process depends on whether you have a gas, electric, or tankless unit. Before you turn anything up, it’s worth knowing that the U.S. Consumer Product Safety Commission recommends a setting of 120°F to prevent scalding. Water at 140°F can cause a burn in one second, and water at 150°F scalds in less than a second. With that context, here’s how to safely increase your hot water temperature.
Adjusting a Gas Water Heater
Gas water heaters are the simplest to adjust. The thermostat is built into the gas control valve, which sits near the bottom of the tank. You’ll see a dial or knob on the front of this valve. Turn it to a higher setting and you’re done.
Some dials show exact temperatures, while others use labels like “Low,” “Medium,” “Hot,” and “Very Hot.” If yours only has labels, check the owner’s manual for the corresponding temperatures. A setting marked “Medium” on many models sits around 120°F, while “Hot” is closer to 130–140°F. Some newer A. O. Smith and similar models have electronic displays that let you select a precise temperature anywhere from 95°F to 150°F.
After adjusting, wait at least 30 to 60 minutes before testing the water at a faucet. Gas heaters recover relatively quickly, but you need time for the full tank to reach the new temperature.
Adjusting an Electric Water Heater
Electric water heaters require a bit more work because the thermostats are hidden behind access panels on the tank itself. Most residential electric models have two thermostats: an upper one and a lower one, each paired with its own heating element.
Start by turning off the circuit breaker that powers the water heater. This is not optional. You’ll be exposing wiring, and electric water heaters run on 240 volts. With the power off, remove the access panel (usually held on by a couple of screws), pull back any insulation, and you’ll see the thermostat. It’s a small device with a temperature dial that you adjust with a flathead screwdriver. Turn it up to your desired temperature, then repeat the process on the second panel if your unit has two.
Set both thermostats to the same temperature. If they’re mismatched, you can get inconsistent water temperatures. Replace the insulation and panels, flip the breaker back on, and wait one to two hours for the full tank to heat up before testing.
If your electric heater has tripped its high limit switch (a safety device that cuts power when the tank overheats), you’ll find a red reset button above the upper thermostat. Press it firmly to reset. If it trips repeatedly, that points to a deeper problem like a faulty thermostat or element, and you’ll need a technician.
Adjusting a Tankless Water Heater
Tankless models are the easiest to adjust. Most have a digital control panel mounted on the front of the unit with up and down buttons. Simply press the up arrow to raise the temperature to your preferred setting. Changes take effect almost immediately since these units heat water on demand rather than storing it.
Choosing the Right Temperature
The standard recommendation of 120°F works well for most households. It’s hot enough for comfortable showers, effective dishwashing, and laundry, while keeping scalding risk low. At 120°F, it takes about four minutes of continuous contact to cause a burn, giving you a reasonable safety margin.
There are legitimate reasons to go higher. If you have a large household that runs out of hot water frequently, bumping up to 130°F lets you mix in more cold water at each fixture, effectively stretching your hot water supply. Households with a dishwasher that lacks its own internal heating element may also benefit from 130–140°F water for proper sanitization.
Bacteria control is another factor. Legionella, the bacterium responsible for Legionnaires’ disease, thrives between 77°F and 113°F and can survive in water below 120°F. The CDC recommends storing hot water above 140°F to prevent Legionella growth, which creates a tension with the CPSC’s 120°F scalding-prevention guideline. One common solution is to set the tank to 140°F and install anti-scald mixing valves at your fixtures, which blend in cold water to deliver a safer temperature at the tap. This approach kills bacteria in the tank while protecting skin at the faucet.
Households with young children, elderly residents, or anyone with reduced sensation in their skin should be especially cautious about settings above 120°F.
When the Problem Isn’t the Thermostat
If you’ve already turned the thermostat up and your water still isn’t hot enough, the setting may not be the issue. Several common problems can make a water heater underperform even when the thermostat reads the right number.
Sediment buildup is the most frequent culprit. Over time, minerals from your water supply settle at the bottom of the tank, forming an insulating layer between the heating element (or burner) and the water above it. This forces your heater to work harder and longer to reach the set temperature, and in some cases it never fully gets there. The signs are pretty recognizable: popping or rumbling noises from the tank, water that takes longer than usual to heat up, a noticeable drop in how much hot water you get before it runs cold, or rusty and discolored hot water. Your energy bills may also creep up without any change in usage.
A failing heating element on an electric unit can produce similar symptoms. If only the lower element has gone out, you might get some hot water but run out quickly. If the upper element fails, you may get barely any hot water at all. A faulty thermostat can also misread the tank temperature and shut off heat too early.
On gas models, a dirty or failing thermocouple, a clogged burner, or poor ventilation can all reduce heating performance. If the pilot light keeps going out, that’s a sign the thermocouple needs attention.
How to Flush Your Tank
If sediment is the likely problem, flushing the tank can restore lost performance. Plan on 30 to 90 minutes for the full process.
- Turn off the power. For electric heaters, flip the circuit breaker. For gas heaters, turn the gas valve to the pilot position or the lowest temperature setting. Never drain a tank with the electric element still powered on, as this will destroy the element.
- Shut off the cold water supply using the valve near the top of the tank.
- Attach a garden hose to the drain valve at the bottom of the tank and run it to a floor drain, a bucket, or outside.
- Open a hot water faucet on a floor above the tank. This lets air into the system and helps water flow out freely.
- Open the drain valve and let the tank empty. This takes 20 to 60 minutes depending on tank size.
- Flush out remaining sediment by turning the cold water supply valve on and off a few times once the tank is mostly empty. This stirs up sediment sitting on the bottom and pushes it toward the drain.
- Watch the water coming out of the hose. When it runs clear, close the drain valve, turn the cold water supply back on, and wait for a steady stream from the open hot water faucet upstairs, which tells you the tank is full.
- Restore power by flipping the breaker or turning the gas valve back to your desired setting.
Flushing once a year keeps sediment from building up enough to affect performance. If you live in an area with hard water, every six months is better. If the drain valve is clogged with sediment and won’t flow, you may need a technician to clear or replace it.