How to Safely Drain an A. O. Smith Water Heater

The Short Version

• Turn off the power source first: shut off the circuit breaker for an electric heater, or turn the gas thermostat dial to Pilot for a gas model.
• Hook a standard garden hose to the drain valve (the threaded spigot at the bottom of the tank) and lead the other end outside or down a basement floor drain.
• Close the cold water supply valve at the top of the tank, then open a hot water tap on an upper floor to break the vacuum (trapped suction that stops water from flowing out).
• Open the bottom drain valve to empty the tank, clear out any sediment (gritty mineral buildup at the bottom of the tank), and refill the unit completely with cold water before turning the power back on.

Safety First: Shutting Off Power, Gas, and Heat

Draining a water heater involves two serious hazards: intense heat and electrical current. The water inside your A. O. Smith tank is typically stored between 120 and 140 degrees Fahrenheit. That is hot enough to cause severe burns within seconds if it splashes onto bare skin. Before touching a single valve, you must disable the heat source and give the unit time to cool, or take strict precautions to handle hot water safely.

For an electric A. O. Smith water heater, walk to your main household electrical panel. Find the double-pole circuit breaker labeled for the water heater (usually a 30-amp breaker) and switch it completely to the Off position. Never rely on the unit's internal thermostat or reset button to shut down power. If an electric water heater is drained while the breaker is still on, the upper heating element will dry fire (heating elements burning out because the tank has no water). A dry heating element burns out and destroys itself in less than thirty seconds without water to absorb the heat.

For a gas A. O. Smith water heater, look at the front of the unit near the bottom. You will see the gas control valve, which is usually a gray box with a temperature knob and a status dial. Turn the temperature knob to its lowest setting, then rotate the main control dial from "On" to "Pilot". Leaving it on Pilot keeps the tiny pilot flame lit so you do not have to relight the burner later, but it prevents the main gas burner from firing up while the tank is empty. If you plan to leave the heater empty for several days or perform plumbing repairs, switch the dial all the way to "Off" and shut the manual gas supply valve on the gas pipe feeding the unit.

Before moving forward, run through this quick safety checklist:

• Confirm the electrical breaker is switched off at the panel, or verify the gas dial sits on Pilot.
• Wear sturdy work gloves and closed-toe shoes to shield your hands and feet from hot water spills.
• Check that children and family pets are kept clear of the drainage path and basement floor.
• If time allows, let the tank sit for two to three hours after cutting power so the water drops to a lukewarm, skin-safe temperature.

Connecting the Hose and Draining the Tank Step by Step

Once the heat source is safely disabled, you can begin the draining process. How you handle the valves depends on whether you are doing a quick maintenance flush to clear loose sand, or a full tank drain to empty the tank completely. The following steps explain how to perform a full drain from start to finish.

1. Inspect the bottom drain valve: Locate the drain valve (the threaded spigot at the bottom of the tank). On an A. O. Smith heater, this valve is either brass with an oval handle or black composite plastic with a slotted turn-screw. Examine the threads to make sure they are clean and free of rust or calcium crust.
2. Attach your garden hose: Thread the female end of a standard 3/4-inch garden hose onto the drain valve spigot. Thread it on carefully by hand first to avoid cross-threading, especially if your heater has a plastic valve. Hand-tighten the hose connection firmly. You can give it a gentle quarter-turn with slip-joint pliers, but do not overtighten plastic threads or you could crack the valve body.
3. Route the discharge hose: Lead the other end of the hose to a safe drainage location. Gravity moves the water out of the tank, so the end of the hose must sit lower than the bottom of the water heater. An outdoor driveway, a gravel garden bed, a sump pump pit, or a basement floor drain works best. If you route the hose outdoors, keep it away from sensitive grass or flowerbeds if the water is still hot. Avoid running the hose into a laundry sink that sits higher than the heater, because water will not flow uphill without a secondary pump.
4. Shut off the cold water supply: Look at the top of your water heater. Find the cold water pipe (marked by a blue plastic ring or located on the right side as you face the heater). Turn the shutoff valve clockwise until it stops. If your pipe has a ball valve with a straight handle, turn the handle ninety degrees so it sits perpendicular across the pipe to block the incoming city water.
5. Open a hot water faucet upstairs: Walk inside to the nearest bathroom or kitchen and open the hot water handle on a sink faucet all the way. This lets air enter the plumbing system. Opening the faucet breaks the vacuum (trapped suction that stops water from flowing out), functioning just like lifting your finger off the top of a liquid-filled straw so the water can flow freely out the bottom.
6. Open the drain valve: Return to the heater. If your drain valve has a brass handle, turn it counterclockwise to open it. If it has a plastic valve with an indented slot, insert a wide flathead screwdriver into the slot and turn it counterclockwise a quarter-turn to a half-turn until water begins rushing through the hose.
7. Monitor the water flow: Listen to the water moving through the hose. At first, the runoff may appear yellow, rusty, or milky, carrying gritty white and brown sediment flecks. Let the water continue draining until the flow slows to a stop and the tank sounds completely hollow when gently tapped near the bottom. A standard 40-gallon or 50-gallon tank usually takes twenty to forty minutes to empty completely.

How to Clear a Drain Valve Clogged by Thick Sediment

If you open the drain valve and only get a sad trickle, or nothing at all, do not assume the tank is already empty. Water heaters naturally collect sediment (gritty mineral buildup at the bottom of the tank) over time. In hard water areas, calcium and magnesium settle out of the heated water and form a heavy layer of sand, flakes, and hardened scale right across the base of the tank. This debris often drifts straight into the narrow mouth of the drain valve and blocks it like a cork.

The safest and cleanest way to clear this blockage is the water pressure blast method. You use the household water pressure to shove the sediment blockage out of the way. While the bottom drain valve and your garden hose remain wide open, walk to the top of the heater and turn the cold water supply valve fully on for five to ten seconds, then shut it off again. The incoming cold water shoots downward through the internal dip tube, churning up the tank bottom with full city pressure. This sudden blast often blows right through the sediment dam, sending a thick rush of brown water and gravel out through the garden hose. You can repeat this quick five-second blast two or three times until water runs freely.

If blasting cold water into the tank does not dislodge the clump, you may need to clear the opening mechanically. First, close the bottom drain valve and unscrew the garden hose. Place a shallow plastic basin or baking pan directly under the spigot, and have old towels ready on the floor. Put on safety glasses and heavy gloves. Slowly open the valve just enough to slide a stiff, straightened wire coat hanger or a long zip-tie straight into the valve opening. Gently push and twist the wire back and forth to break up the crusty mineral plug. As soon as the wire pokes through the crust, hot water will begin surging out around the wire, so pull the wire back and close the valve immediately. Reattach your garden hose tightly, open the valve back up, and let the broken debris flush out through the hose.

Be gentle with factory plastic drain valves. If the valve feels stuck or jammed with grit, do not grab a heavy wrench and muscle it open. Plastic valve stems can snap off inside the fitting, causing an uncontrollable flood of hot water onto your floor. If a plastic valve refuses to turn smoothly under normal hand or screwdriver pressure, stop what you are doing and close the cold water supply before proceeding further.

Refilling the Tank Correctly to Prevent Dry Firing

Refilling an A. O. Smith water heater requires patience and the correct sequence. The single most common and costly mistake homeowners make during maintenance is restoring power or lighting the burner before the tank is completely full of water. If electricity reaches an exposed heating element in an empty or half-filled tank, the element will overheat and melt instantly. Follow these exact steps to refill the unit safely:

1. Close the drain valve: Turn the bottom drain valve clockwise until it is completely seated. If you are turning a plastic screw-slot valve, tighten it until it stops, but do not force it past its natural stopping point. Unscrew the garden hose and check the spigot nozzle for any lingering drips.
2. Keep the upstairs hot water faucet open: Make sure the hot water tap you opened earlier (at a sink or bathtub) remains wide open. Do not close it yet. As the tank fills from the bottom, air inside the tank needs an open pathway to escape so your plumbing lines do not become air-locked.
3. Turn on the cold water supply valve: Slowly open the cold water shutoff valve at the top of the tank all the way. You will immediately hear water rushing into the steel cylinder.
4. Purge the trapped air: Walk to the open faucet inside the house. Within a few minutes, you will hear loud hissing, sputtering, and coughing as trapped air is forced through the pipes ahead of the rising water. The faucet will spit air bursts mixed with cloudy water. This is completely normal.
5. Wait for a solid, unbroken stream: Let the faucet run until the sputtering stops entirely and a smooth, solid stream of cold water flows from the spout for at least one full minute. This steady stream confirms that the tank is 100 percent full of water and that all air pockets have been pushed out. Once the flow is completely steady, turn the sink faucet off.
6. Check the tank for leaks: Return to the heater and inspect the drain spigot, the cold water inlet valve, and the temperature-and-pressure relief valve. Verify that the bottom drain valve is completely dry and not weeping water.
7. Restore power or gas: Now that you have verified the tank is entirely full, it is safe to turn the heat back on. For an electric unit, switch the circuit breaker back to the On position at your breaker panel. For a gas unit, turn the gas control knob from Pilot back to your desired temperature mark (the factory recommended setting is typically 120 degrees Fahrenheit).

When to Stop and Call a Plumber

Most water heater drains go smoothly, but certain warning signs indicate that simple maintenance has uncovered a deeper mechanical failure. If you encounter any of the following problems, shut the cold water supply valve, leave the power off, and call a licensed plumbing professional:

• A drain valve that will not stop leaking: If water continues to drip from the drain valve after you have closed it completely, the internal rubber washer may have rotted or sharp sediment grains may have scored the brass seat. A plumber will need to replace the faulty valve with a durable full-port brass ball valve.
• Water leaking directly from the tank body: If you spot water pooling under the heater jacket, oozing from the lower access cover, or weeping along bottom welded seams, the internal glass lining of the tank has cracked and rusted through. Draining will not resolve this problem; a rusted tank cannot be repaired and must be replaced.
• A stuck or leaking temperature-and-pressure relief valve: The safety valve on the top or side of the heater (the brass valve with a small test lever) should never leak steadily. If it drips constantly or sticks in the open position, the valve has failed and cannot safely protect your home against excess pressure.
• Persistent gas odors or pilot failures: If you smell raw gas around a gas heater, do not attempt to light the pilot or operate light switches. Leave the home immediately and call your local gas utility from outside. If the pilot simply refuses to stay lit after repeated attempts, the thermocouple or electronic spark igniter likely requires professional replacement.

Proper clearances and steady ambient conditions around your utility appliances also make routine maintenance far safer. For homeowners managing appliances in colder outbuildings or utility spaces, maintaining steady room warmth with a dependable garage heater with a thermostat helps prevent pipes from freezing during winter plumbing work. Similarly, if your unit is installed in a compact manufactured housing utility closet, careful attention to ventilation and clearance, much like choosing a heater for a mobile home, protects your living space from excess moisture and heat buildup.

FAQs

How often should an A. O. Smith water heater be drained or flushed?

A. O. Smith recommends flushing or draining the tank once every year under normal household water conditions. If your home has hard municipal water or private well water with heavy mineral content, performing a quick sediment flush every six months helps prevent scale buildup, protects the lower electric heating element, and keeps heating efficiency high.

What is the difference between draining a water heater and flushing it?

A full drain empties every gallon of water out of the tank with the cold water supply shut off, which is necessary when replacing heating elements, swapping out the anode rod, or replacing the heater. A flush leaves the cold water supply valve turned on while the bottom drain valve is opened for a few minutes, using city water pressure to stir up and blast loose sediment out without completely emptying the tank.

Can I drain my water heater into a standard plastic bucket?

You can use a bucket for a brief five-second test to see if sediment is clearing, but draining an entire 40-gallon or 50-gallon tank with five-gallon buckets is dangerous and messy. The water leaving the heater is scalding hot, buckets fill in less than a minute, and carrying heavy sloshing containers across a basement creates an extreme burn and slip hazard. Always use a heat-resistant garden hose routed to a floor drain or outdoor area whenever possible.

Why does my water smell like rotten eggs when draining the tank?

A sulfur or rotten egg smell during draining is caused by a chemical reaction between naturally occurring sulfates in your water supply and the sacrificial anode rod inside the tank. The magnesium or aluminum rod reacts with bacteria in warm water to produce hydrogen sulfide gas. If the odor is strong, a licensed plumber can inspect the tank and replace a standard magnesium rod with an aluminum-zinc alloy rod to neutralize the smell.