THE SHORT VERSION
- Smell gas? Leave now. Don’t touch light switches, don’t use a phone inside, don’t start a car in the garage. Call the gas company or 911 once you are well away from the house.
- Carbon monoxide alarm? Get everyone outside to fresh air first, then call 911. Don’t go back in until the fire department says it’s clear.
- Water leaking? Close the cold water valve on the pipe above the heater (or the main shutoff). Then turn the gas control knob to OFF or switch off the heater’s breaker, but only if you can reach it without standing in water.
- Relief valve gushing hot water, or water scalding hot? Turn the gas knob to OFF or the breaker off and call a plumber. Never cap or plug the relief valve or its pipe.
- Sparks, smoke or a burning smell? If there is fire or smoke, get out and call 911. If not, switch off the breaker from a dry spot and call an electrician or plumber.
Start here: which emergency is it?
Answer in order and stop at the first yes. The first three put people at risk, so they come before floors or the heater.
You smell gas: leave first, call from outside
Utilities add a “rotten egg” odorant to natural gas so you can smell a leak. A spark from a light switch, doorbell, garage door opener or phone can ignite it; the federal pipeline safety agency (PHMSA) lists cell phones as an ignition source.
Get everyone out
Don’t switch anything on or off on the way, don’t light anything, and don’t start a car in an attached garage.
Call from a safe distance
From a neighbor’s house or down the street, call your gas company’s emergency line or 911. Rheem, A.O. Smith and Bradford White manuals all say to call the gas supplier from a neighbor’s phone, and the fire department if you can’t reach it.
Wait for the all-clear
Go back in only when the gas company or fire department says so. If gas was shut off at the meter, let the utility turn it back on.
Bradford White warns that the odorant can fade and some people can’t smell it well. If that’s your household, ask the gas company about a gas detector.
Carbon monoxide alarm: fresh air first, then 911
Carbon monoxide (CO) is the odorless gas from incompletely burned fuel. A gas water heater with a blocked or disconnected vent can spill it indoors. CPSC’s instruction: get outside to fresh air immediately, then call 911. CDC warns that people who are asleep can die from CO before they notice symptoms, so treat a night-time alarm as real.
- Symptoms (CPSC): headache, dizziness, weakness, nausea, vomiting, sleepiness, confusion. CDC notes they are often mistaken for flu.
- Count heads outside and stay out until emergency services have aired out the house and given the all-clear, as Kidde, a CO alarm maker, advises.
- Find the source before relighting anything. Kidde says to call a qualified appliance technician if the alarm sounds again within 24 hours.
A clue on a gas tank: A.O. Smith says water dripping at the draft hood (the metal cone on top) means a vent problem; contact the gas utility.
Water leaking or flooding: stop the water, then the heat
A slow drip and a gushing tank start the same way. Rheem tells owners to have the installer show them the gas shutoff; if no one did, the diagrams below show where the controls usually are.
Check that the floor is safe
CDC’s flood guidance: turn off power only from a dry spot. If water is near outlets, cords or the panel, or you’d have to stand in water to reach it, stay out and call an electrician or your electric utility.
Close the cold water valve above the heater
Turn a round handle clockwise until it stops, or turn a lever a quarter turn so it sits across the pipe. If it won’t move, close the house’s main water shutoff.
Turn off the heat
Gas: turn the control knob on the front to OFF (A.O. Smith notes it must be pressed in slightly to leave PILOT; don’t force it). Electric: switch off the heater’s breaker, usually a double breaker labeled “water heater,” or a disconnect switch beside the heater.
Relieve pressure and contain the water
Open a hot tap somewhere in the house to take pressure off the tank, and leave the relief valve lever alone. Then towels, buckets and a wet/dry vacuum; move belongings off the floor.
Relief valve spraying or dripping: never cap it
The temperature and pressure (T&P) relief valve is the brass valve near the top of the tank, with a pipe running toward the floor. It dumps water if the tank gets too hot (A.O. Smith says it is normally rated for 210°F) or the pressure too high (150 psi on A.O. Smith’s tanks). It is what keeps an overheated tank from bursting, which is why every manual says never to cap or plug it or its pipe.
| What you see | Usual cause | What to do now |
|---|---|---|
| Occasional drips, often after heating | Pressure: thermal expansion or high house pressure, the most common cause per A.O. Smith | Not an emergency. Bucket under the pipe, book a plumber; see relief valve leaking. |
| Bursts of very hot water or steam | Overheating: a failed thermostat (gas), or a shorted element or thermostat (electric) | Heat off, stay clear of the pipe, call a plumber today. |
| Won’t stop running | Debris on the seat or a worn valve | Close the cold valve, heat off, call a plumber. |
Sources: A.O. Smith Technical Bulletin 52 and A.O. Smith gas and electric use & care manuals.
Scalding water or a heater that won’t shut off
Water far hotter than usual, steam at the taps or a burner that never stops means a control has failed. Rheem and A.O. Smith both say to shut the manual gas valve if the heater overheats or the gas won’t shut off. Electric tanks have an energy cut-off (ECO), a high-limit switch with a red reset button on the upper thermostat, that cuts power when the water gets too hot; A.O. Smith says not to restore power until the cause is fixed.
Shut off the heat
Gas: knob to OFF, then close the gas shutoff valve if the burner still runs. Electric: breaker off.
Keep everyone off the hot taps
A.O. Smith’s manual says children, the elderly and people with disabilities are at highest risk.
Call a plumber
A failed thermostat, element or gas control is a repair, not a reset.
| Water temperature | First-degree burn | Second- or third-degree burn |
|---|---|---|
| 122°F | 1 minute | 5 minutes |
| 131°F | 5 seconds | 25 seconds |
| 140°F | 2 seconds | 5 seconds |
| 149°F | 1 second | 2 seconds |
| 154°F | Instantly | 1 second |
Source: CPSC memorandum (1978), reproduced in A.O. Smith’s gas water heater manual. For a safe setting afterward, see water heater temperature.
Sparks, smoke or a burning smell from an electric heater
Electric tanks run on 240-volt circuits. A burning or melted-plastic smell, scorch marks at the access panels or junction box, or a breaker that keeps tripping point to a wiring or element fault.
- Flames or smoke: leave and call 911. The U.S. Fire Administration says to use an extinguisher only on a small, contained fire with a clear way out; electrical fires need a Class C or A-B-C extinguisher.
- Smell or sparks, no fire: switch off the heater’s breaker from a dry spot. Don’t open the panels or touch the wiring.
- Then call an electrician or plumber. Oregon’s State Fire Marshal lists a burning or rubbery smell from an appliance as a reason to call an electrician.
On a gas heater, A.O. Smith says soot around the burner means turning the gas off until it is repaired.
Draining a leaking tank (or leaving it to the plumber)
Draining keeps a leaking tank from emptying onto the floor, and manufacturers describe it for owners. It is also how people get burned. If the plumber is coming within a few hours and the water is contained, waiting is fine.
Heat off first
Gas knob to OFF or breaker off. A.O. Smith says an element powered without water around it burns out (“dry fire”).
Let it cool
A.O. Smith says to let the water run cool before draining, which can take 10 minutes or more. With the cold valve closed the tank cools slowly, so expect hot water.
Hose to a drain
Attach a garden hose to the drain valve near the bottom and run it to a floor drain, outdoors lower than the valve, or a bucket. Rheem warns the water can scald.
Let air in, then open the drain
Open a hot tap elsewhere in the house so air can enter, then open the drain valve. Keep hands and face clear.
If nothing comes out, stop
A.O. Smith notes sediment can clog the drain valve. Close it and leave it to a professional.
Is it the tank or a fitting?
It decides the bill. A.O. Smith’s puddle bulletin lists the usual sources: condensation, the drain valve, the relief valve, the pipes on top, gas valve threads, electric element gaskets, and the tank itself. All but the last are usually fixable. Water running down from the top usually means a pipe or valve; water from underneath with dry pipes above often means the tank.
Photograph where the water is before you mop. Then see water heater leaking to trace it and repair or replace for what each answer means.
Water damage: you have 24–48 hours
EPA’s guidance is to dry water-damaged areas and items within 24–48 hours to prevent mold. It is a guideline: EPA notes mold won’t always grow after 48 hours, and can grow even if things dry sooner. Its table covers clean water, which is what a water heater leaks.
| Material | EPA’s advice |
|---|---|
| Carpet and pad | Extract water with a wet vacuum, run a dehumidifier and fans |
| Drywall | Can be dried in place if it isn’t swollen and seams are intact; otherwise remove and replace |
| Ceiling tiles, fiberglass or cellulose insulation | Discard and replace |
| Concrete or block | Wet vacuum, then dehumidifiers, fans or heaters |
| Vinyl, tile, linoleum | Vacuum or wipe, let dry; check underneath for trapped water |
| Wood surfaces | Remove moisture right away, dry with dehumidifiers, gentle heat and fans |
Source: EPA, Mold Remediation in Schools and Commercial Buildings, Table 1. EPA suggests professional help for mold over about 10 square feet.
Document it for insurance before cleanup erases it
Homeowners policies typically cover sudden, accidental water damage from an appliance but not the appliance itself, Travelers explains, and a long-ignored leak may not be covered. The National Association of Insurance Commissioners (NAIC) says to notify your insurer right away (deadlines vary by state) and that you are expected to protect your home from further damage. So stop and dry the water, but photograph it first.
Capture this today
- Photos and video of the water, the heater and where the water came from, before you mop
- A close-up of the heater’s rating plate (model and serial number), which also gives its age and warranty status
- A list of damaged items and rooms
- Receipts for fans, dehumidifier rental and any emergency plumber
- Who you spoke to at the insurer, and when
- Ask the insurer before the old heater is hauled away
Home warranties work differently; see insurance and home warranties.
Getting it replaced fast without overpaying
ENERGY STAR warns that an emergency replacement “can be more expensive” and tends to limit you to standard models. Home Depot’s published range for an installed gas or electric tank is $1,600–$2,400, and it says it often installs tanks the same day at no extra charge if you call before noon on a weekday within 30 miles of a branch. This Old House lists $200–$500 for after-hours or weekend installation where contractors charge it.
Ask before anyone starts work
- Is there an after-hours fee, and how much?
- What exact model (brand, model number, gallons) are you installing? Same fuel and size as mine?
- Does the price include the permit, haul-away and code updates (expansion tank, drain pan, venting, straps)?
- Are you licensed and insured? (The FTC suggests checking the license with your state or county.)
- Can I have the total in writing, by text or email, before you start?
- How much is due today? The FTC advises never paying the full amount up front.
On a newer heater, check the warranty by serial number first. Under A.O. Smith’s warranty, a tank that leaks within its term gets a new comparable heater, but the owner usually pays the labor and the manufacturer doesn’t cover water damage.
Hot water in the meantime
- Stove or kettle for washing up. Never use a camp stove, grill or portable gas heater indoors; CDC lists them as carbon monoxide hazards.
- Cold water still works if you closed only the valve at the heater, not the main.
- A gas heater that only lost its pilot, with no leak or gas smell, can often be relit by following the label on the tank; see pilot light problems.
- Showers elsewhere for a day can beat paying an after-hours premium.
Common questions
Can a water heater explode?
It can if the temperature and pressure relief valve can’t open, which is why manufacturers say never to cap or plug it or its pipe. A working valve opens before the tank reaches a dangerous temperature or pressure. If it is discharging hot water, turn off the heat and call a plumber.
Should I turn off the water heater if it’s leaking?
Yes. Close the cold water valve above it, then turn the gas knob to OFF or switch off the breaker. Don’t touch electrical equipment while standing in water; call an electrician or your utility instead.
What do I do if my water heater smells like gas?
Leave without switching anything on or off, then call the gas company or 911 from outside. Don’t look for the leak or relight the pilot. Go back in only when the gas company or fire department says it is safe.
Why is water coming out of the pipe on the side of my water heater?
That is the relief valve’s discharge pipe. A few drips usually mean high pressure from thermal expansion; bursts of very hot water mean the tank is overheating, so turn off the heat. Call a plumber either way, and never cap the pipe.
Can I keep using a water heater that was in a flood?
No. Rheem and A.O. Smith say not to use a gas water heater if any part has been under water, and to replace it rather than repair it. A.O. Smith says the same for an electric heater with submerged thermostats.
How fast can I get a water heater replaced?
Often the same day for a same-type tank; Home Depot says it can often install the same day if you call before noon on a weekday. Heat pump models can take longer because the installer may need to order one, ENERGY STAR notes.
Sources
Sources checked October 4, 2026. Prices, codes and rebates change. Check current details with your installer and local permit office.
- Recognizing and Responding to Pipeline Emergencies (natural gas do’s and don’ts) ↗ · U.S. DOT Pipeline and Hazardous Materials Safety Administration
- Natural Gas Safety ↗ · Kansas Corporation Commission
- Gas Emergencies ↗ · Pennsylvania Public Utility Commission
- Emergency gas shut-off ↗ · San Diego Gas & Electric
- Propane safety: what to do if you smell gas ↗ · N.C. Department of Agriculture & Consumer Services, Standards Division
- Carbon Monoxide Information Center ↗ · U.S. Consumer Product Safety Commission
- About Carbon Monoxide Poisoning (January 2026) ↗ · CDC
- What should I do when my carbon monoxide alarm sounds? ↗ · Kidde
- Safety Guidelines: Reentering Your Flooded Home (August 2026) ↗ · CDC
- Signature 100 gas water heater installation instructions and use & care guide 100341468 (2021) ↗ · A.O. Smith
- Residential electric water heater installation instructions and use & care guide ↗ · A.O. Smith, hosted by Lowe’s
- Hybrid electric heat pump water heater installation instructions and use & care guide ↗ · A.O. Smith, hosted by Lowe’s
- Technical Bulletin 52: Leaking temperature and pressure relief valve ↗ · A.O. Smith
- Technical Bulletin 51: Puddle on floor ↗ · A.O. Smith
- Low NOx gas water heater use & care manual AP16412-1 (2017) ↗ · Rheem, hosted by InspectAPedia
- Service manual 238-51542-00C, Defender FVIR gas water heaters (2019) ↗ · Bradford White, hosted by G.T. Sanders
- Fire extinguishers ↗ · U.S. Fire Administration
- Basement and garage fire safety ↗ · U.S. Fire Administration
- Electrical fire safety brochure (2023) ↗ · Oregon State Fire Marshal
- Burns: first aid (reviewed April 2026) ↗ · MedlinePlus, U.S. National Library of Medicine
- A Brief Guide to Mold, Moisture and Your Home ↗ · U.S. EPA
- Mold Remediation in Schools and Commercial Buildings, Table 1: Water damage cleanup and mold prevention ↗ · U.S. EPA
- What you need to know when filing a homeowners claim ↗ · National Association of Insurance Commissioners
- A Consumer’s Guide to Home Insurance ↗ · National Association of Insurance Commissioners
- Answers to 5 common insurance questions about home water damage ↗ · Travelers
- Residential limited warranty 100286376 (retailer copy, 2018) ↗ · A.O. Smith
- Heat pump water heaters ↗ · ENERGY STAR
- When Should You Replace Your Water Heater? (2024) ↗ · ENERGY STAR
- Cost to Replace a Water Heater (installed ranges, same-day installation) ↗ · Home Depot
- How Much Does Water Heater Installation Cost? (updated June 17, 2026) ↗ · This Old House
- How To Avoid a Home Improvement Scam (2022) ↗ · Federal Trade Commission