House smells like gas, but the utility found no leak
Last reviewed · Not medical advice
If the utility tested and found no gas, the likeliest culprit is sewer gas: hydrogen sulfide from a dry drain trap or drain slime smells almost the same as the gas odorant. Next is a water heater reacting with its anode rod, which only affects hot water. Work through the list in order: refill traps, do the hot-versus-cold water test, check outside, then batteries, animals, and new materials. If the smell comes back stronger or near a gas appliance, call the utility again — a no-leak result is for that moment only.
Most likely causes
Ranked for this situation. Open any cause for checks and fixes.
- 1
Dried-out drain trap
most commonTop suspect after a no-leak visit — sewer gas is the classic gas impostor.
Points to this:- Smell is near a guest bath, basement floor drain, unused shower, or utility sink
- Started after a trip, or in a room nobody uses
- Goes away after running water
Check it, fix it, who to call
Safe checks- Run water in every sink, tub, and shower for 30 seconds, and pour a bucket of water into floor drains.
- Flush toilets that rarely get used.
- Wait a few hours. If the smell is gone, it was a dry trap.
Fix- Run water in rarely used fixtures every couple of weeks.
- For floor drains that dry out constantly, a plumber can fit a trap primer or a trap-seal insert.
DIY stops here: If refilling the traps doesn't stop it within a day, the problem is past the trap — call a plumber.
Who fixes it: Plumber
More on this - 2
Slime in a sink drain or overflow
most commonSulfur smell right at one sink or shower drain.
Points to this:- Smell is right at one sink or shower, strongest with your nose at the drain
- The drain is slow
- The overflow hole under the sink rim smells when you sniff it
Check it, fix it, who to call
Safe checks- Sniff the drain opening, then the overflow hole, separately.
- Pull the pop-up stopper — it's often coated in sludge.
Fix- Clean the stopper; scrub the drain and overflow with a long brush.
- Flush with very hot water. Use an enzyme drain cleaner for ongoing buildup.
DIY stops here: If cleaning doesn't change the smell, look for a trap or vent problem.
Who fixes it: You (DIY)
More on this - 3
Water heater reaction (sulfur in hot water)
commonOnly when hot water runs, at every hot tap.
Points to this:- Only the hot water smells; cold water from the same faucet is fine
- Worse after the heater has sat unused, or after a vacation
Check it, fix it, who to call
Safe checks- Fill one glass with hot water and one with cold, step away from the sink, and smell each.
- Check whether the smell appears at every hot tap (water heater) or just one (that fixture's drain).
Fix- Flush the water heater.
- Have a plumber replace the magnesium anode with an aluminum-zinc or powered anode.
- Ask a plumber about sanitizing the tank.
DIY stops here: Anode replacement on a gas or electric heater is usually a plumber job — you're working with gas lines or 240V and a pressurized tank.
Who fixes it: Plumber
More on this - 4
Gas smell drifting in from outside
commonSame dayDrifts in from outside — your utility may not have checked a neighbor's line or the street.
Points to this:- Smell is stronger outdoors or near the meter than inside
- Comes and goes with the wind, or started when nearby digging began
Check it, fix it, who to call
Safe checks- Note where outside it is strongest, then call the gas utility — outdoor leaks are their job too.
Fix- The utility locates and repairs outdoor and street leaks.
DIY stops here: Report it; don't dig, touch the meter, or probe around lines.
Who fixes it: Your gas utility's emergency line
More on this - 5
Blocked or damaged plumbing vent
commonWithin daysIf drains gurgle.
Points to this:- Drains gurgle or bubble, especially when a toilet flushes
- Water levels in toilet bowls drop or fluctuate
- Smell in several rooms, worse on windy days
Check it, fix it, who to call
Safe checks- Flush a toilet and listen at nearby sinks and tubs for gurgling.
- Look at the roof vent from the ground with binoculars for a nest or debris (don't climb onto the roof).
Fix- A plumber clears the vent stack or repairs a cracked or disconnected vent pipe.
DIY stops here: Roof work and snaking vents are a job for a plumber.
Who fixes it: Plumber
More on this - 6
Hydrogen sulfide in well water
less commonPrivate wells: hot and cold both smell.
Points to this:- Home is on a private well
- Both hot and cold water smell, at every faucet
Check it, fix it, who to call
Safe checks- Compare hot and cold glasses at several taps; have the well water tested.
Fix- Water treatment, e.g. aeration, oxidizing filters, or chlorination, sized to the test results.
DIY stops here: Choose treatment from a lab test, not a guess.
Who fixes it: Plumber
More on this - 7
Dead animal in a wall, attic, or crawlspace
less commonRotten-sweet, at one wall or ceiling, fades over weeks.
Points to this:- Rotten or sickly-sweet smell concentrated on one wall or ceiling area
- Flies appearing indoors; recent rodent activity
Check it, fix it, who to call
Safe checks- Sniff along walls to find the strongest spot; check attics, crawlspaces, and behind appliances.
Fix- Remove the animal if you can reach it (wear gloves).
- Otherwise pest control can locate and remove it; ventilate while it fades.
DIY stops here: Opening walls or entering attics with insulation: pest control or a handyman.
Who fixes it: Pest control
More on this - 8
Overcharging lead-acid battery
rareSame dayNear a battery backup or charger.
Points to this:- Smell near a battery backup unit, battery charger, or in the garage
- Battery case swollen or hot
Check it, fix it, who to call
Safe checks- Find any lead-acid batteries in the house; feel the case from a distance for heat (don't touch a swollen one).
Fix- Disconnect the charger at the outlet if it's safe to reach.
- Replace the battery and have the charger checked.
DIY stops here: A hot, swollen, or hissing battery: ventilate, keep away, and call the fire department if it's smoking.
Who fixes it: Licensed electrician
More on this - 9
New paint, flooring, furniture, or cleaners
rareA chemical smell some people read as gas, after paint, flooring, or furniture.
Points to this:- Started after a renovation, a delivery, or deep cleaning
- Strongest in the room with the new item
Check it, fix it, who to call
Safe checks- Ventilate and see if it fades over days. Make sure products weren't mixed (bleach plus ammonia is dangerous).
Fix- Ventilate; run fans; let new items air out in a garage or outdoors where possible.
DIY stops here: If you feel unwell, leave the area and ventilate; contact Poison Control or a clinician if symptoms persist.
Who fixes it: You (DIY)
How we rank causes: by how often each one explains this smell in ordinary homes, according to plumbing, HVAC, electrical, and building-science guidance, adjusted for the context on this page. The labels are judgments, not measured statistics. Anything dangerous that can't be ruled out (gas, fire, electrical) is covered in the safety box at the top of the page, whatever its rank.
Which one is it?
| If the smell… | Check next |
|---|---|
| Is gone after running water everywhere | It was a dry trap — done |
| Comes from the drain, not the water | Clean drain and overflow |
| Is only in hot water | Water heater anode |
| Is stronger outdoors or with windows open | Outside source — call the utility about outdoors |
| Comes with gurgling drains | Plumbing vent |
| Is rotten-sweet at one wall | Dead animal |
| Started after a renovation or delivery | New materials off-gassing |
Narrow it down
Answer in order. Stop at the first yes.
- 1Is the smell back, stronger, or near a gas appliance?Yes → Call the utility again from outside. Don't work this list.No → Start the elimination order.
- 2After refilling every trap, is the smell gone within a few hours?Yes → Dry trap. Keep water in rarely used drains. Go thereNo → Keep going.
- 3Does only hot water smell (two-glass test)?Yes → Water heater. A plumber can swap the anode rod. Go thereNo → Keep going.
- 4Is it stronger outside the house?Yes → Report it to the utility as an outdoor odor.No → Check batteries, look for rodents or a dead animal, and think about recent renovations.
Safe checks you can do yourself
In the order that finds the source fastest.
- 1
Ask what the utility checked
Utility technicians typically test the air, the meter, the service line, and accessible appliance connections. Ask whether they checked every gas appliance and whether they checked outside. Note the date and time of the visit.
- 2
Refill every trap
Run each sink, tub, and shower for 30 seconds, flush every toilet, and pour water into floor drains. Then wait a few hours with the house closed up.
- 3
Two-glass water test
Hot glass and cold glass, smelled away from the sink. Hot only → water heater. Both → water supply. Neither → drains.
- 4
Smell log
For a few days, note when and where you smell it: morning or night, after showers, with the HVAC on, windy days. Patterns point at the source — and help the utility or a plumber if you call back.
- 5
Outside walk
Walk the perimeter, the meter area, and the street. A stronger smell outside means an outdoor source.
Why a no-leak visit doesn't end the question
The technician tested what was there at that moment. Intermittent sources — a trap that dries out every few weeks, a vent that misbehaves on windy days, a water heater that smells after sitting overnight — may not be present during the visit. That's why a smell log helps. It's also why a returning or stronger smell is a reason to call again, not to second-guess yourself.
If only you can smell it
If nobody else in the home smells it, the utility found nothing, and the smell follows you from room to room, mention it to a clinician. Smell perception can change for many reasons. This isn't something to diagnose online — just don't rule it out.
When DIY stops
- The smell returns stronger or near a gas appliance — that's a utility call, not DIY.
- Anode replacement, vent clearing, and camera inspections — plumber work.
- An overheating or swollen battery.
Who to call
- Your gas utility's emergency line
The smell comes back, gets stronger, or is outdoors.
Checks for natural gas leaks. Call its emergency number, not the billing line.
- Plumber
Traps keep drying out, drains gurgle, or hot water smells.
Drains, traps, toilets, vents, water heaters, and leaking supply lines.
- Sewer / drain specialist
A smoke test to find where sewer gas is escaping.
Camera inspection and smoke testing of sewer lines and vents.
- Pest control
You suspect a dead animal in a wall or ceiling.
Finds and removes mice and rats, and seals entry points.
Answer a few questions about where and when you smell it. You'll get the causes ranked for your situation.
Frequently asked questions
Can sewer gas smell like natural gas?
Yes. Sewer gas contains hydrogen sulfide, and the odorant in natural gas is another sulfur compound. Most people can't tell them apart by smell, which is why a dry drain trap is the most common answer after a no-leak visit.
The gas company found nothing, but I still smell it. Should I call again?
Yes, if it returns stronger, appears near an appliance, or you hear hissing. Tell them it's a repeat call and when you notice it most.
Why do I smell gas only at night or in the morning?
Closed-up houses concentrate smells. Traps also dry out slowly, and water heaters smell after sitting. A log of when it happens usually narrows it down.
Could my water heater smell like gas even if it's electric?
Yes. The rotten-egg smell from the anode rod reaction comes from the water, not from gas, so electric heaters can do it too.
Related smells
Sources
- Using Natural Gas Safely — American Gas Association
- Carbon Monoxide Information Center — U.S. CPSC