Water Heater Smells Like Gas: What to Do Right Now

The Short Answer: If the air around your water heater smells like rotten eggs or sulfur, treat it as a gas leak. Get everyone out now, without touching light switches, phones, or anything that could spark. From outside, away from the building, call 911 or your gas utility (or propane supplier). Do not look for the leak, and do not go back in until responders say it is safe.

What to do right now

1. Get everyone out, including pets. Do not stay behind to open windows or look around.
2. Do not create a spark or flame. PG&E’s guidance is not to use anything that could be an ignition source, “including cell phones, flashlights, light switches, matches or vehicles” (PG&E gas safety (opens in a new tab)). That includes the water heater’s controls, the thermostat, and doorbells or garage door openers.
3. Call from a safe place. PG&E says to call 911 and then the utility. Your utility’s emergency number is on your bill and its website. For propane, call your propane supplier, or 911 if you cannot reach them.
4. Do not hunt for the leak. Do not sniff around fittings, spray soapy water on connections, tighten anything, or try to turn the heater’s gas control off. Locating and repairing a leak is the responders’ and a licensed gas technician’s job.
5. Stay out until you are told it is safe, and do not relight the water heater or any other appliance yourself afterward unless the responder or technician tells you it is ready.

A. O. Smith’s water heater label gives the same core instructions: do not try to light any appliance, do not touch any electric switch or use any phone in the building, and call your gas supplier from a neighbor’s phone, or the fire department if you cannot reach the supplier (A. O. Smith manual 100366722 (opens in a new tab)).

Why water heater closets and garages need extra caution

A gas water heater sits next to its own gas connection, valve and burner, and many have a pilot flame or an igniter that can turn on without warning. In a small closet, a leak has little room to spread out. The same closet also has to supply air for combustion, which is why the installation manual specifies air openings for confined spaces and warns against storing gasoline, solvents or paint nearby. The A. O. Smith label tells owners to smell for gas next to the floor before operating the heater, “because some gas is heavier than air and will settle on the floor.”

Gas, or something else?

Utility gas and propane have no smell of their own; an odorant is added so you notice a leak. Other water heater odors can be confused with it. If you cannot tell, treat it as gas. Other odors are covered in the water heater smells guides.

The rotten-egg hot water explanation comes from A. O. Smith’s manual: four conditions together (sulfate in the water, little dissolved oxygen, sulfate-reducing bacteria in the tank, and active hydrogen from the anode) produce the smell. The same manual says a small amount of smoke and odor during initial start-up is normal from oil burning off metal parts. Neither should be used to talk yourself out of a gas smell in the air.

Carbon monoxide is a separate danger

Carbon monoxide has no color or smell, so you cannot detect it the way you can detect gas. The CPSC lists headache, fatigue, shortness of breath, nausea and dizziness as early symptoms, names water heaters among the appliances that can produce it when malfunctioning, and says that if a CO alarm sounds you should move outside to fresh air, call 911, and not re-enter until responders allow it (CPSC fact sheet (opens in a new tab)). An exhaust smell, soot at the draft hood, or a damaged vent pipe means the heater should be shut down and inspected. For more, see water heater carbon monoxide leaks.

Propane homes: two extra cautions

• The smell can fade. The Mississippi State Fire Marshal’s propane brochure describes odor fade, a reduction in the odorant that can be caused by air, water or rust in a tank or cylinder, or by leaking propane passing through soil. It advises responding to even a faint odor and adds that some people have trouble smelling propane because of age, a medical condition, or medications (propane safety information (opens in a new tab)).
• Detectors help. The same brochure suggests UL-listed propane gas detectors as an added layer, installed per the maker’s instructions, and says never to ignore the smell even if a detector is silent.

Tankless and outdoor heaters

The same rules apply to a tankless unit in a closet, basement or garage: if the room smells like gas, leave and call. With an outdoor unit, step well away and call; do not open its cover. A smell that comes only from a tankless vent while it is firing is covered in tankless exhaust smells like gas.

After the area is declared safe

The utility or fire department checks the building and may shut off the gas supply or tag the appliance. A licensed gas technician then repairs the leak, tests the gas piping and connector, and checks the heater’s gas control, burner, and venting before relighting it. If the smell started right after a new installation, see gas smell after water heater replacement. Have fuel-burning appliances inspected yearly, as the CPSC recommends.

Frequently Asked Questions

Q: The smell is faint and only in the closet. Do I still need to leave? A: Yes. A faint smell can still be a leak, a small closet can concentrate gas, and propane odor can fade. Responders can measure gas levels; your nose cannot judge whether it is safe.

Q: Should I turn off the gas at the water heater before I leave? A: No. Leave first. Reaching the heater’s gas control means staying where the gas is. Let the utility or fire department decide where and how to shut off the supply.

Q: My hot water smells like rotten eggs but the closet does not. Is that a gas leak? A: Probably not. When the smell is only in the hot water and the air around the heater smells normal, the usual cause is the anode reacting with sulfate and bacteria in the water. If you notice the smell in the air at all, treat it as gas.