Where Is the Reset Button on an AO Smith Water Heater?

Look behind the upper metal access panel on your electric tank

On an electric AO Smith water heater, two metal plates are screwed into the side of the tank. The red reset button is always located behind the upper metal plate, known as the access panel (a metal plate screwed onto the side of the tank). It is never behind the lower plate.

Behind that top plate, the button sits protected by fiberglass or foam insulation and a clear plastic guard. Mounted against the steel tank is the upper thermostat and the high-limit switch (a red safety button that shuts off power if the water gets dangerously hot).

On almost every AO Smith electric model, this button is bright red, round, and about the size of a pencil eraser. It rests near the center of the upper thermostat bracket, right above the temperature dial.

Placing this button at the top is intentional. Warm water rises, so the top reaches peak temperatures first. The sensor sits at the top to catch dangerous heat spikes before steam pressure damages your plumbing.

If you open the lower panel, you will only find the lower heating element (a metal rod inside the tank that warms the water) and its thermostat dial. All safety shutoffs run through the red button behind the upper panel.

Shut off the electrical power before touching any tools or panels

Before touching your water heater with a tool, you must cut the electrical supply. Residential electric water heaters run on 240 volts of electricity, which is twice the voltage of a standard wall outlet. Touching live wire terminals inside an open panel can cause severe injury or fatal electrical shock.

Go to your home electrical service panel and find the circuit breaker (a switch in your home electrical panel that cuts power to the unit) labeled for the water heater. In most homes, this is a double-pole breaker switch rated for 30 amps. Push the switch firmly into the full "Off" position. If the breaker is not labeled clearly, verify power with a non-contact voltage sensor at the tank wires before proceeding.

Never touch the panel if water has pooled on the floor around the heater. Make sure your hands are dry, wear rubber-soled shoes, and avoid leaning bare skin against the metal tank jacket.

Follow these safe steps to press the red reset button

Once you confirm the circuit breaker is off, you can safely open the upper panel and reset the high-limit switch. Follow these steps:

1. Remove the upper metal plate: Use a flathead screwdriver or a 1/4-inch nut driver to remove the screws holding the upper access panel. Set the screws aside and pull the metal cover away from the tank.
2. Fold back the protective insulation: Behind the metal plate, you will see foam or fiberglass insulation. Carefully fold this insulation outward to expose the components underneath. Wear thin gloves if your unit has fiberglass so the material does not irritate your skin.
3. Locate the plastic safety cover: AO Smith includes a clear plastic shield over the upper thermostat to guard against touching electrical terminals. Look through the plastic opening near the top of the bracket to spot the red button.
4. Press the red button firmly: Place your thumb on the red button and press inward. If the switch had tripped, you will feel and hear a distinct click. That click confirms the contacts reconnected. If the button feels loose without clicking, the switch did not trip, or the water is still too hot to reset.
5. Reinstall the insulation and access panel: Tuck the insulation back into the cavity and secure the metal access panel with its screws. Never restore power while internal wiring is exposed.
6. Flip the circuit breaker back on: Return to your electrical panel and switch the water heater breaker back to "On."
7. Wait for the water to heat: A standard 40-gallon or 50-gallon tank needs roughly 45 to 60 minutes to reheat cold water. Check a nearby hot water faucet after an hour to confirm warm water has returned.

Check the control valve and pilot if you own a gas model

Gas AO Smith water heaters do not have a red reset button. Gas units heat water using an open flame burner rather than electric elements, so their safety systems rely on gas valves and thermal sensors instead of electrical switches.

If your gas water heater is not heating water, check these components instead:

• The gas control valve status light: Modern gas heaters have a control box mounted low on the front of the tank. A green light flashing every three seconds indicates normal operation. If the light flashes a repeating pattern, check the diagnostic chart on the valve sticker to find the fault code.
• The pilot light flame: Look through the small glass sight window at the bottom of the tank near the burner chamber. If you do not see a small blue flame, your pilot has gone out. Relight it by turning the control knob to "Pilot," pushing the knob down, and clicking the spark igniter until the flame stays lit.
• The blower switch on power-vent models: If your gas water heater has a black plastic blower motor on top that vents outside through white plastic pipes, you own a power-vent model. These units plug into a 120-volt wall outlet. Turning the rocker switch on the blower housing off for 30 seconds and back on resets the control board.
• The thermal cutoff switch: Modern gas heaters have a thermal cutoff switch near the burner that shuts off gas flow if the air intake screen clogs with lint. If this safety link opens, it requires a replacement sensor rather than a button reset.

Find out why the safety switch tripped before turning power back on

A tripped reset button is never an everyday occurrence. The high-limit safety switch cuts power only when water temperatures inside the tank exceed 170 to 180 degrees Fahrenheit. Water that hot causes severe scald burns within two seconds. While an electrical storm can occasionally trigger the switch, an equipment failure is usually the true cause.

A shorted heating element is the most common culprit. Over years of use, the metal casing around an electric heating element can split. Water seeps into that split, allowing electrical current to bypass the thermostat. The element heats continuously until the water reaches dangerous temperatures and trips the red button.

A stuck thermostat is another frequent problem. Water heater thermostats rely on internal contacts that open and close as water temperature changes. Over time, electrical arcing can weld these contacts together. When a thermostat welds shut, it feeds continuous power to the element, forcing the safety switch to cut power.

Heavy mineral sediment can also cause the switch to trip. Minerals like calcium settle to the bottom of the tank, forming scale around the lower element. This sediment traps heat inside the tank bottom, which travels up the steel tank jacket and trips the upper safety switch. If your water heater sits in an uninsulated garage, pairing regular tank flushing with an electric heater for a garage with a thermostat helps maintain stable room temperatures and prevents rapid thermal swings around plumbing pipes. Similarly, water heaters in manufactured housing often sit in narrow utility closets; if you are managing climate control across the home, choosing the right heater for a mobile home ensures surrounding utility alcoves stay dry and warm.

Finally, loose wiring connections behind the access panel generate electrical resistance. This resistance creates localized heat right at the thermostat bracket, tripping the switch even if the water inside the tank is cool.

Stop pressing the button and call a professional if these warning signs appear

You can safely reset the red button once to see if a temporary power surge caused the shutdown. But you should never treat this button like an everyday light switch. Forcing a tripped switch back on without fixing the root cause creates serious hazards, including melted wiring and electrical fires.

Stop resetting your AO Smith water heater and call a licensed plumber or electrician if you notice any of these warning signs:

• The button pops back out within hours or days: If the water heater trips again soon after a reset, you have a shorted element, a stuck thermostat, or heavy sediment buildup that requires physical repair.
• Water is present inside the access panel: If you see water droplets or damp insulation around the wiring terminals, stop immediately. Water leaking past element gaskets into electrical connections creates a serious risk of fire and shock.
• Melted wire insulation or burnt odors: If you smell burned plastic or spot black scorch marks on terminal screws, electrical resistance has damaged the controls. Do not restore power until a professional replaces the damaged parts.
• The button will not click or stay in: If pressing the red button yields no click, or if it springs back out immediately after the tank cools, the internal switch contacts have burned out and the thermostat assembly must be replaced.
• Boiling noises or water blasting from the relief valve: If you hear loud rumbling sounds inside the tank or see hot water discharging from the temperature and pressure relief pipe, shut off power and water immediately.

Check these common questions before calling for service

What should I do if the red reset button will not stay pushed in?

If the button springs back out immediately, the water inside the tank may still be above 170 degrees Fahrenheit, which prevents the safety contacts from latching. Turn off the circuit breaker, open a hot water tap for ten minutes to flush out boiling water, and let the tank cool for an hour before trying again. If the button still refuses to latch once the tank is cold, the switch has failed internally and requires a replacement upper thermostat assembly.

How can I verify if an element or thermostat caused the trip?

You can confirm the root cause by turning off power, disconnecting the wires from each heating element, and measuring resistance with an electrical multimeter set to ohms. A healthy residential heating element typically reads between 11 and 16 ohms, while a burned element will show zero resistance or no continuity to the metal base. If both elements measure normal resistance and show no shorts to ground, one of the thermostats has stuck contacts and needs replacement.

Can an electrical storm cause the reset button to trip?

Yes, a severe thunderstorm, power surge, or sudden brownout on the electrical grid can trip the sensitive high-limit switch on an electric water heater. A momentary voltage spike creates high current across the upper thermostat contacts, triggering the thermal cutoff even if the water temperature is safe. If you reset the button once after a storm and the unit operates smoothly for weeks, a utility power surge was the likely cause.

Is there a reset button on an AO Smith hybrid heat pump water heater?

AO Smith hybrid electric heat pump water heaters still use standard backup heating elements, so they retain a physical red reset button behind the upper access panel just like standard electric tanks. However, heat pump units also feature an electronic display screen on the front that reports error codes for compressor or airflow faults. You can clear most minor electronic heat pump faults by cycling the circuit breaker off for 60 seconds or using the digital control panel.