Hot Water Heater Troubleshooting -
Rotten Egg Odor


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Why does my hot water heater smell like sulfur or rotten egg?

Use hot water heater troubleshooting guide to see why, what is the cause of stinky water and how to fix the problem.

Rotten egg odor can occur to any tank-type water heater, either gas or electric, as long as they are equipped with the metal tank and anode rod.

Rotten egg smell cause

Possible cause of the sulfur or rotten egg smell coming from water heater is the bacteria developed in the tank sediment, a breeding ground for the bacteria that is fed from hydrogen sulfide or H2S gas, created from decay of anode rod.

Three components are required to generate hydrogen sulfide gas that make water heaters smell like rotten egg: sulfur, hydrogen, and bacteria. And right there is the solution; if any of the above elements is removed there should be no stinky water smell.

Public (municipality) water supplies, when properly chlorinated, will kill the bacteria and the odds are you won't have this problem. But if using the well water, the problem might be there.

Every heater with the metal tank is equipped with the anode rod, usually called sacrificial rod, and is used to protect the steel metal tank from corrosion and rust. Because of its nature to dissolve due to the aggressive water action, it sacrifices itself to protect the tank.

If the heater is to remain unused due to vacation and for an extended period of time, turn the power off, not only to conserve energy but to prevent a build-up of hydrogen gas. The situation is aggravated by hard water and by leaving the tank unused for long periods.

Hydrogen sulfide gas is distinctive and its presence can significantly affect the taste and odor of the water. Developed bacteria can be accompanied by black deposits, the result of pipe and fitting corrosion. Extremely high concentrations are toxic.

The increased level of sulfur, presence of hydrogen, water with little or no dissolved oxygen and temperatures below 138 F or 59 C are creating the environment where bacteria will develop significantly.

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Stinky water and rotten egg solution

Just adding a water softener to treat your hard water is not a solution. It can make the problem even worse, especially if using the well water and during long periods of no water movement.

Since the problem comes from the chemical reaction between magnesium or aluminum decomposing sacrificial anode and surrounding, removing the rod is definitely not recommended.

Keep in mind that complete removal of the anode rod will void the warranty and shorten tank life.

Solution for the rotten egg odor is simple and cheap, but not permanent. Frequent flushing the sediments out from the heater is what we recommend and useful for the performance and efficiency at the same time. Use chlorine bleach or peroxide.

Use the next steps when flushing the system with hydrogen peroxide:

  • Shut off the cold water valve to the heater
  • Open hot water tap
  • Drain the tank
  • Open plumbing on one side and pour 2 liters of 3% hydrogen peroxide solution to 40 gallon of water. Let it stay for few hours
  • Close the plumbing
  • Turn the cold water on and let the water run from the tap

Either using chlorination or peroxide flush, this is a surface treatment where repeated trials are recommended for highly infected plumbing systems.

Another solution might be softening the water, but the problem is the increased anode consumption and the amount of hydrogen sulfide gas produced.

Try also replacing the standard magnesium or aluminum anode rod with zinc-alloy.

Note: Buying a plastic lined tank type heater like Rheem Marathon might be a good solution if stinky water is consistent in your household plumbing.

In this or any other case, hot water heater troubleshooting might be easy but we always suggest calling a plumber or licensed technician, or they can call you - if you fill out this form.

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