Quick Answer:
If you smell something when you run hot water after a recent water heater install, it’s usually not the tap water being contaminated from your supply. Start by flushing the new heater exactly as the installer or manufacturer’s instructions say to remove manufacturing residues, then run hot water at several fixtures to purge lines. Do a simple smell test comparing hot and cold at the same tap to narrow the problem to the heater or the house plumbing. If odors are only on the hot side after flushing, check the sacrificial anode and confirm the installer didn’t accidentally connect or cross hot lines with a drain or waste line.
Why This Happens
- New tanks sometimes contain oil, protective coatings or manufacturing residues that produce odors when first heated.
- Hot water can activate smells that are not noticeable in cold water — some chemical and bacterial reactions happen at higher temperatures.
- A failing or incorrect sacrificial anode can produce metallic or rotten‑egg–like smells inside the tank.
- Mistakenly connected piping or a cross‑connection during installation could let sewer or waste odors reach hot taps, though this is rare.
- If you’ve recently changed a filter or other equipment, compare problems to similar posts like Smell after filter install for patterns.
Step-by-Step What to Do
1. Flush the new water heater per the install instructions
Follow the manufacturer’s or installer’s flushing procedure to clear manufacturing oils and residues. If you’re unsure what the instructions say, contact the installer or the manufacturer rather than guessing. For gas or electric units, turn off the heating source before you start any tank work — if you’re not comfortable doing this, have the installer return.
2. Run hot water at multiple fixtures to purge the lines
- Open a hot tap at the sink, then run hot water at showers and other faucets for several minutes to move any trapped air or residue out of the piping.
- Flush each fixture long enough that the water runs hot and steady — often 5–10 minutes is sufficient for most homes.
3. Smell-test hot vs cold lines
- At the same fixture, run cold water and notice any odor. Then run hot water and compare. If only hot water smells, the source is likely the heater or hot-side plumbing.
- Test several fixtures. If the smell appears only at some taps, check the local supply and faucet connections for those fixtures.
4. Check the sacrificial anode
A failing or wrong type of anode rod can cause metallic or rotten odors. Don’t try to remove the anode unless you know how and the heater is safely de‑energized. Instead, visually inspect what the installer documented or ask them to confirm the anode type and condition. If the anode is the issue, replacing it often clears the odor.
5. Verify there is no cross‑connection between sewer and hot lines
- Look for obvious mistakes first: open attic or crawlspace access and visually check that the hot outlet from the heater goes to house plumbing and not to any drain pipes or vents. Do not crawl into confined spaces alone or without proper precautions.
- Signs of a cross‑connection include sewer‑type odors only from hot taps and a sudden onset of smell immediately after the install. If you suspect wrong piping, stop using the hot water and call your installer or a plumber.
What Not to Do
- Avoid turning the heater up to very high temperatures to “burn off” smells — that risks scalding and won’t fix manufacturing residues, anode problems, bacterial growth, or incorrect piping.
- Don’t ignore persistent hot‑water‑specific odors. Call a professional if odors continue after a proper flush or if you suspect the installer made a piping mistake.
- Do not attempt major repairs on gas or electric heaters unless you are qualified. Improper work can be dangerous.
When to Call a Professional
- If flushing and purging lines don’t stop the odor and the smell is clearly tied to hot water.
- If you smell sewer or sewage‑like odors from hot taps — this could be a cross‑connection or misrouted piping and needs a plumber’s inspection.
- If you see signs of tank corrosion, suspect the anode rod has failed, or you’re uncomfortable performing any of the recommended checks safely.
Safety Notes
- Turn off gas or electric power to the heater before doing any work that involves opening ports, draining the tank, or touching wiring. If you don’t know how, have a pro do it.
- When draining the tank, attach a hose and run it to a safe drain location — hot water can scald and damage surfaces.
- Avoid confined spaces without proper lighting and ventilation. If you must inspect piping in an attic or crawlspace, use a helper and take slip and fall precautions.
- If you detect a strong chemical or sewer smell in the house that you can’t identify, ventilate the area and call a plumber for an inspection rather than trying untrained fixes.
Common Homeowner Questions
- Q: The smell is only when I run hot water — is my drinking water contaminated?
A: If cold water does not smell, the supply is likely fine; the source is the heater or hot plumbing. - Q: How long will any installation smell last?
A: Often a few days to a couple of weeks after a proper flush and line purge; persistent smells need inspection. - Q: Can I fix this myself?
A: You can flush the tank and run hot water at fixtures, but call a professional for anode issues, suspected cross‑connections, or if you’re unsure about shutting off power or gas.
More in this topic
For more related fixes and similar symptoms, see Sewer Gas Smell from Floor Drains.