Water heater smells like sulfur? Top causes and proven fixes

Does your water heater smell like sulfur whenever you run hot water? If you’ve noticed a sulfur odor in hot water, it’s time to address the issue before it worsens. A sulfur smell is often a sign of hydrogen sulfide gas building up in your water heater, and there are several reasons this could happen. We’ll break down the most common causes, offer troubleshooting steps, and share the best solutions to get rid of that sulfur smell for good.

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The information provided in this article may not apply to your specific appliance model. While we strive to offer helpful advice for DIY appliance repairs, variations in models and configurations can lead to differences in troubleshooting steps, error codes and part replacements. For the most accurate guidance, we strongly recommend consulting the technical sheet for your specific appliance model.

Common reasons your water heater smells like sulfur

If your water heater’s sulfur smell is persistent, here are the top reasons this issue may arise:

Bacterial growth in the water heater

Over time, bacteria can grow in the warm, moist environment of the water heater tank, especially when it hasn’t been used for a while. These bacteria feed on the naturally occurring sulfates in the water, producing hydrogen sulfide gas as a byproduct, leading to that rotten egg smell. Keeping the water heater set to at least 140°F (60°C) will make it harder for bacteria to grow. However, be mindful of the risk of scalding at higher temperatures.

This issue is more common in homes with well water, as it typically has higher sulfate content.

Magnesium or aluminum anode rods

Most water heaters are fitted with an anode rod to prevent corrosion in the tank. However, magnesium and aluminum rods can react with the sulfate in the water, leading to the production of hydrogen sulfide gas. This reaction is often responsible for the hot water sulfur smell, especially in areas with high sulfate levels.

If the smell only occurs when using hot water, it’s a strong indication that the anode rod is the source.

High sulfur content in your water supply

In some cases, the sulfur smell isn’t directly related to the water heater but is due to high sulfur levels in your water supply. This can affect both hot and cold water, but the heat intensifies the odor, making it more noticeable in hot water. If this is the case, you may need to consider a water filtration system to remove excess sulfur from your water.

How to troubleshoot  

If your water heater smells like sulfur, follow these troubleshooting steps to identify and resolve the issue:

Step 1: Test the cold water supply

First, determine whether the sulfur smell is present in both your cold and hot water. Run the cold water tap to see if the odor is noticeable. If the smell is only present in hot water, the issue is likely in the water heater. If both cold and hot water smell like sulfur, the problem may stem from your water supply.

Step 2: Replace the anode rod

1. If you have an electric water heater, switch off the breaker at your electrical panel. For gas water heaters, turn the gas valve to the “off” position.
2. The anode rod is typically located on the top of your water heater and can be accessed by removing the hexagonal head cap or by unscrewing it from the top of the tank.
3. To prevent any water spills, attach a garden hose to the drain valve at the bottom of the tank and drain a few gallons of water.
4. Use a wrench to remove the old anode rod from the water heater tank. Be cautious as the rod may be corroded and require some force to loosen.
5. Carefully insert the new anode rod into the opening at the top of the water heater tank. Use a suitable replacement anode rod. Consider using a zinc-aluminum alloy or powered anode rod, which is known for its effectiveness in reducing odor-causing bacteria.
6. Use a wrench to tighten the rod securely into place to prevent leaks.
7. Close the drain valve and allow the tank to refill with water. Check for any leaks around the anode rod area.
8. Once the tank is filled, turn on the power or gas supply to the water heater.

Step 3: Flush the water heater tank

1. Turn off the water heater and let it cool down. For gas heaters, set the gas control valve to the “pilot” position.
2. Locate the drain valve on the tank. It is typically located near the bottom and looks like a hose bib with a threaded end.
3. Attach a garden hose to the valve and run it to a drain, utility sink, or outside.
4. Open a hot water faucet in your home to allow air into the system and help with drainage.
5. Open the valve and allow the tank to drain completely. Be cautious as the water can be hot.
6. To further flush the tank, turn the cold water supply back on for a few minutes while the drain valve is still open. This helps to flush out any remaining sediment that may be settled at the bottom of the tank.
7. Once the water runs clear and you have flushed the tank adequately, close the drain valve by turning it clockwise.
8. Disconnect the hose from the drain valve.
9. Turn on the water supply to refill the tank. Keep the hot water faucet open to release any air trapped in the system.
10. For electric heaters, switch the power back on at the breaker box. For gas heaters, set the gas control valve back to the desired temperature.

Step 4: Disinfect the tank

1. Turn off the water heater and drain the tank as described earlier.
2. Turn off the cold water supply valve to prevent more water from flowing into the tank while you drain it.
3. Attach a garden hose to the water heater’s drain valve (located at the bottom of the tank). Place the other end of the hose in a nearby drain, bucket, or outside. Open the drain valve and allow the tank to empty. Be careful, as the water inside can be very hot. 
4. Once the tank is empty, close the drain valve. Pour about 1-2 pints of 3% hydrogen peroxide into the tank through the anode rod port or cold water inlet. 
5. This amount should be enough to sanitize a typical 40-gallon tank. For larger tanks, you may need to increase the amount of peroxide.
6. Open the cold water supply valve and let the tank fill back up with water. The hydrogen peroxide will mix with the water inside the tank, allowing it to clean the interior surfaces.
7. Allow the water and hydrogen peroxide mixture to sit in the tank for 2-4 hours. This gives the peroxide enough time to kill off any bacteria causing the rotten egg smell.
8. Drain the tank again to flush out the hydrogen peroxide and any remaining bacteria. Refill the tank with fresh water and repeat the flushing process until the water runs clear and odor-free.
9. Once the tank is thoroughly flushed, close the drain valve and let the tank fill up with water again. Turn the power or gas back on and let the water heater resume normal operation.

Step 5: Install a water filtration system

If the sulfur odor originates from your water supply, a whole-house water filtration system may be necessary. This system can reduce the sulfur content in your water, preventing both hot and cold water from smelling like sulfur.

Additional information

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