Quick Answer:
A sulfur or “rotten egg” smell right after installing a new water heater is common and often not a sign the unit is defective. Flush several hot taps after heater install to clear factory residues and trapped water; this often removes oils, packaging residues and stagnant water that produce odors. If the smell remains after flushing, the cause is usually bacterial action on the anode rod or an existing issue in the home plumbing.
Why This Happens
- Factory residues and oils from manufacturing, packaging or transport can be released when the heater gets hot. These usually clear with flushing.
- Hydrogen sulfide (a rotten-egg odor) forms when certain bacteria react with the water and the heater’s sacrificial anode—magnesium anodes are a common trigger.
- Disturbed scale or trapped stagnant water in pipes can release smell when first heated.
- Similar smells appear after other changes to the plumbing system; see Egg smell after long vacation and Egg smell after installing filter for related situations.
Step-by-Step What to Do
Step 1 — Initial flush (first and most important)
- Turn on the hot tap closest to the heater and let it run for 3–5 minutes, then open other hot taps (kitchen, bathroom, shower) to flush more lines. Flush several hot taps after heater install to clear factory residues.
- Run the shower on hot for several minutes; showering fixtures often hold more stagnant water and show the smell more clearly.
- Be cautious: water will be hot. Keep the thermostat at a safe setting (around 120°F / 49°C) while flushing to reduce scald risk.
Step 2 — Isolate where the smell is strongest
- Check multiple fixtures. If the odor is only at one tap, the issue is likely that fixture or its supply line rather than the heater.
- If all hot fixtures smell, the heater or hot plumbing loop is the likely source.
Step 3 — Consider anode-related causes
- Many new smells are linked to the sacrificial anode reacting with bacteria. If the heater has a magnesium anode, that can make hydrogen sulfide more likely.
- Do not remove or change the anode unless you’re comfortable and follow the manufacturer instructions. If you suspect the anode, ask a plumber about replacement options (aluminum/zinc or powered anodes reduce odor in some cases).
Step 4 — If flushing doesn’t help: disinfecting and deeper cleaning
- Shock chlorination can address bacterial growth; this is a common remedy but involves chemicals and careful flushing afterward. Follow the heater manufacturer guidance or hire a professional if you’re not experienced.
- Do not mix household chemicals; ventilate the area and follow safety directions on any product used.
Step 5 — Monitor and document
- After flushing and any adjustments, give the system 24–48 hours and check again. Note when and where the smell appears—time of day, fixtures affected, and whether cold water has any odor.
- If the odor gradually fades, it was likely residues or trapped water. If it returns or worsens, proceed to the next step.
What Not to Do
- Do not replace a new heater without flushing residues first.
- Do not attempt gas burner adjustments, thermostat wiring or other gas/electrical repairs unless you are qualified—turn off utilities and call a professional.
- Do not pour chemicals down the drain without following manufacturer guidance; improper use can damage plumbing and pose health risks.
- Do not ignore scald risks when running hot water—supervise children and the elderly during testing.
When to Call a Professional
- The smell persists after thorough flushing and basic checks (24–48 hours).
- You detect other problems: discolored water, leaks, sputtering, or loss of hot water capacity.
- If you’re uncomfortable performing anode inspection, shock chlorination, or any work that requires shutting off gas or power.
- If you smell gas or suspect a combustion issue—stop using the appliance and call a licensed technician immediately.
Safety Notes
- Always turn off the heater’s power source (electric breaker or gas control) before doing internal work. If unsure, hire a pro.
- Avoid burns: run water at a moderate temperature and test before placing hands under a hot stream.
- Use gloves and eye protection if handling anode rods or chemicals. Ensure good ventilation for any chlorination or chemical treatment.
- Follow manufacturer instructions for maintenance and warranty requirements—incorrect service can void warranties or create hazards.
Common Homeowner Questions
- Why does it smell like rotten eggs? Bacteria reacting with the anode rod can produce hydrogen sulfide; factory residues or trapped water can also cause temporary odors.
- How long should flushing take to work? Often a few minutes to a couple of hours of regular use; allow 24–48 hours for complete dissipation in some cases.
- Can I safely fix this myself? Simple flushing and checking fixtures are safe; anything involving gas, electricity, or chemical disinfection is best done by a licensed plumber if you’re unsure.
For more related articles, see the Sulfur / Rotten Egg Smell in Water hub.