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Water Heaters · Tank Water Heater

Water Heater Pilot Light Won’t Stay Lit? 7 Causes and Fixes

Pilot goes out when you let go of the knob, or hours later? Check the relighting steps, drafts and combustion air first. Safe checks and when to call.

By Evrenus Fırat PolatEditor & ResearcherPublished Checked against 2 manuals + 5 manufacturer pages + 1 government source + 1 safety source + 1 industry source

Quick answer

NoticeSmell gas? Leave now and call 911 and your gas company from outside. Don't relight the pilot.

Smell gas? Stop. Leave the house. Call 911, then your gas company, from outside.

When the pilot dies as soon as you release the knob, the flame sensor (thermocouple) or the way you relit it is the usual cause. When it dies hours or days later, look at drafts, blocked air openings and the gas supply. Relight it once by the label. If it goes out again, call a gas pro.

Check these first:

  1. Did you hold the knob in long enough?
  2. Drafts from a door, window or fan
  3. Dust or lint at the base air openings
Time to fix
15–45 min
Difficulty
Moderate, 2 of 4
Safety
DangerGas, Carbon monoxide
On this page · 12 sections

A pilot that won't stay lit is a safety system doing its job. A small sensor in the pilot flame keeps the gas valve open, and when it stops sensing heat, the valve shuts the gas off. A. O. Smith says this is why a pilot that goes out is usually safe, but it still needs a cause.⁠[1] The timing tells you most: does it die the moment you let go of the knob, or hours later? For the parts named here, see how a gas tank heater works. If the pilot never lights in the first place, read a pilot that will not light at all.

Before you start

NFPA's advice is short: if a pilot goes out again and again or is hard to light, there may be a safety problem. Don't try to fix it yourself, and have a fuel gas professional relight it.⁠[2] This guide follows that line. You relight once by the label, you check what you can see from outside the heater, and you leave the gas parts to a pro.

Shut-offs

  • Gas

    The shutoff valve on the gas pipe next to the heater. Turn it off only if you are confident doing so; if you smell gas, leave instead.

  • Water

    The valve on the cold water line above the heater. You don't need to close it for a pilot problem.

Read the lighting label on the heater before you start. A. O. Smith says the label and your manual come before any general guide, because steps differ by model.⁠[1]

You'll need

  • LED work flashlight

Why the pilot goes out

The pilot, the thermocouple and the gas valve sit together at the bottom of the heater, behind the burner access door. The flue and vent carry the exhaust up and out. The diagram marks those parts.

Fig. 1Parts of a gas tank water heater
Parts of a gas tank water heaterFront view of a gas tank water heater with the front cut away to show the inside. Nine numbered parts: 1 flue running up through the center of the tank to the vent; 2 cold inlet pipe on top, left; 3 hot outlet pipe on top, right; 4 anode rod hanging from a port on top; 5 T&P valve on the upper right side with its discharge pipe running down to just above the floor; 6 dip tube carrying cold water down inside the tank; 7 gas valve on the front; 8 burner under the tank; 9 drain valve near the bottom.123456789FlueCold inletHot outletAnode rodT&P valveDip tubeGas valveBurnerDrain valve

  1. Flue and vent Pro only

    On a gas heater, hot combustion gases from the burner rise through a flue in the center of the tank and leave through the vent on top. A poorly vented water heater can leak carbon monoxide into the home, so vent problems are work for a pro.[6][2]

  2. Cold water inlet and shutoff DIY

    Cold water enters on top. The shutoff valve on this line stops the tank from refilling. Close it whenever the heater leaks.[4][7] Where to shut it off: Cold water inlet and shutoff

  3. Hot water outlet DIY

    Heated water leaves from the top of the tank. Its fitting, like the cold one, is one of the places a heater can leak.[4][8] Fix a dripping fitting: Hot water outlet

  4. Anode rod DIY with care

    A metal rod that slowly corrodes so the glass-lined tank does not. A. O. Smith says to pull it for inspection every 3 years, or every year with softened water.[4] If the port leaks: Anode rod

  5. Temperature and pressure (T&P) relief valve and discharge pipe Test only; a pro replaces it

    This safety valve opens to release water if the tank gets too hot or the pressure climbs too high; it is normally rated for 210°F and no more than the tank’s working pressure, generally 150 psi. Its discharge pipe must end no more than 6 inches above a floor drain, or outside, and must never be capped or plugged.[9][4] T&P valve checks: Temperature and pressure (T&P) relief valve and discharge pipe

  6. Dip tube Pro only

    The cold inlet feeds a tube that carries incoming water down toward the bottom of the tank. That lets the heated water rise to the top, where the outlet draws it off.[10][4]

  7. Gas control valve and thermostat Pro only

    The gas control valve holds the thermostat that sets the water temperature. A. O. Smith and NFPA point to about 120°F to lower the risk of scalds.[4][2] If it is wet here: Gas control valve and thermostat

  8. Burner Pro only

    On a gas heater the burner sits under the tank and heats the water from below. An electric heater has no burner; heating elements do the job instead.[6]

  9. Drain valve DIY

    Used to drain the tank and flush out sediment. A. O. Smith recommends draining and flushing every 6 months.[4] If it drips: Drain valve

  • Electric models. An electric tank has no burner, gas valve or flue. Most have two heating elements, wired so they do not heat at the same time.[6]
  • Rating plate. The rating plate on the tank lists the model and serial numbers you need for parts, service and warranty questions.[4]
Original diagram. Simplified — your unit may look different.

When the pilot goes out tells you where to look. Bradford White's service manual sorts the causes the same way: a pilot that won't stay lit when you release the button points to the thermocouple circuit, and a pilot that goes out now and then points to air, venting or gas supply.⁠[3]

The table below comes from Bradford White's troubleshooting chart and A. O. Smith's pilot page.⁠[3]⁠[1]

When the pilot goes outLikely causesWho checks it
As soon as you release the knobKnob not held long enough, or a weak, loose or badly placed thermocoupleYou relight once; a pro tests the thermocouple
After heating cycles, or once a day or weekNot enough combustion air, a blocked vent, unsteady gas supplyYou clear the area; a pro checks vent and gas pressure
After a door opens or a fan runsA draft blowing out the flameYou find and stop the draft
The status light stays on after you turn the knob off (some electronic gas controls)The control is not ready to relight yetYou wait for the light to go out, and at least 10 minutes

  1. Pilot not relit the way the label says

    Most commonDIYTime: 15 min

    The knob was released too soon, or the gas had no time to clear before relighting.
    Fix it: Pilot not relit the way the label says

  2. A draft blows the flame out

    CommonDIYTime: 10 min

    An open door, window or fan near the heater.
    Fix it: A draft blows the flame out

  3. Not enough combustion air

    CommonDIY with careTime: 20 min

    Dust, lint or stored items block the air openings at the base.
    Fix it: Not enough combustion air

  4. Gas supply problem

    Less commonDIY with careTime: 10 min

    A partly closed valve, an empty propane tank or low gas pressure.
    Fix it: Gas supply problem

  5. Weak or loose thermocouple

    CommonPro only

    The flame sensor no longer holds the gas valve open.
    What a pro does: Weak or loose thermocouple

  6. Vent problem or downdraft

    Less commonPro only

    Exhaust can't leave, or air pushes down the vent.
    What a pro does: Vent problem or downdraft

  7. Faulty gas control valve

    Less commonPro only

    The valve's safety parts have failed.
    What a pro does: Faulty gas control valve

Relight the pilot exactly as the label says

The most common reason a fresh relight fails is the relighting itself. A. O. Smith's steps start with the gas off and a wait of at least 10 minutes, so built-up gas can clear before you add a flame. A. O. Smith also notes that modern heaters have a fail-safe that stops the pilot from lighting when the heater has an airflow problem.⁠[1]

  1. Smell for gas before you touch the knob

    • Time: 1 min

    If you smell gas, stop here and leave. A. O. Smith says never to relight a pilot when you smell gas.⁠[1]

    You'll know it worked when: No gas smell anywhere around the heater, including near the floor.

  2. Turn the gas control knob off and wait 10 minutes

    • Time: 10 min

    On a model with a status light that stays on after you turn the knob off, wait until the light goes out before you relight, as Bradford White's chart says.⁠[3]

    You'll know it worked when: The knob is at OFF and 10 minutes have passed.

  3. Set the knob to Pilot and push it fully in

    • Time: 2 min

    Light the pilot as the label says. On an electronic model, keep the knob in and press the igniter button about once a second, for up to 90 seconds. On a manual model, use a long lighter.⁠[1]

    You'll know it worked when: The knob is pressed in about 1/4 inch and held there.

  4. Release the knob slowly and watch the flame

    • Time: 2 min
    • LED work flashlight

    Hold the knob in for the time the label gives, then release it. Turn the knob to On or your setting and check that the flame is large and steady.⁠[1]

    You'll know it worked when: The pilot keeps burning after you let go.

  5. Check the status light on electronic models

    • Time: 1 min

    A. O. Smith says the light must flash once a second for the heater to work. After three failed tries, go to the status light section of the manual.⁠[1]

    You'll know it worked when: The status light flashes once per second.

If the pilot goes out the moment you let go after a careful relight, stop. That pattern points to the thermocouple or the gas valve, which is work for a gas pro.⁠[3]⁠[2]

Still not fixed? Next likely cause: A draft blows the flame out

Stop drafts near the heater

A. O. Smith names drafts as a common cause. A heater in a garage or a utility room with an outside door is most at risk.⁠[1]

  1. Note what happened just before it went out

    • Time: 5 min

    Look for doors that open to the outside, open windows, a box fan, a dryer or an exhaust fan near the heater.

    You'll know it worked when: You know if a door, window or fan was in use at the time.

  2. Keep the door closed and the area still

    • Time: 5 min

    Close windows near the heater and move fans away. Don't block any air openings while you do it; the heater needs that air to burn safely.⁠[4]

    You'll know it worked when: No moving air reaches the burner door.

If drafts keep coming from the vent pipe itself, that is a different problem; see the vent section below.

Still not fixed? Next likely cause: Not enough combustion air

Clear the combustion air openings

A gas burner needs a steady supply of air. A. O. Smith says that without enough air the heater may not burn its fuel properly.⁠[1] Bradford White's first check for a pilot that goes out now and then is the same: make sure there is enough combustion air and clear the jacket openings of dirt, dust and other blockages.⁠[3]

  1. Turn the gas control knob to off

    • Time: 2 min

    Follow the "to turn off gas" part of the lighting label.

    You'll know it worked when: The pilot and burner are off before you clean near them.

  2. Move stored items away from the heater

    • Time: 10 min

    A. O. Smith's manual says combustible items such as clothing, cleaning products and flammable liquids must not be placed against or next to the heater. Gasoline and other flammable vapors must not be stored near it.⁠[4]

    You'll know it worked when: Nothing leans on the heater or sits near its base.

  3. Vacuum dust and lint at the base

    • Time: 10 min

    A. O. Smith's manual says to vacuum around the base for dust, dirt and lint on a regular basis.⁠[4] Don't take the burner or any inner screen apart; that is service work.⁠[3]

    You'll know it worked when: The air openings around the base are clean.

  4. Relight once by the label

    • Time: 15 min

    Use the steps in the relighting section above.

    You'll know it worked when: The pilot stays lit through a full heating cycle.

Laundry rooms and garages make lint and dust build up fast. A quick vacuum at the base each time you check the heater keeps the air path open.

Still not fixed? Next likely cause: Gas supply problem

Check the gas supply

A. O. Smith says gas pressure changes usually settle quickly, and ongoing trouble often starts outside the heater, in the gas lines.⁠[1] A gas supply problem can stop the burner and put the pilot out.⁠[5]

  1. Check that the gas valve is open

    • Time: 2 min

    A. O. Smith's first gas checks are a lit pilot and an open gas valve.⁠[5] Look at the valve on the gas pipe next to the heater, without forcing it.

    You'll know it worked when: You know the shutoff valve next to the heater is open.

  2. Check other gas appliances

    • Time: 5 min

    If other gas appliances also fail, the problem is likely in the gas lines, not the heater.⁠[1] Call your gas company.

    You'll know it worked when: You know if the stove or furnace also has trouble.

  3. Check the propane level on a propane system

    • Time: 5 min

    Call your propane supplier if the tank is low or empty.

    You'll know it worked when: The tank gauge shows enough fuel.

A. O. Smith also lists two supply faults you can't fix from outside the heater: a kink or clog in the flex tube between the gas supply and the gas control, and a dirty pilot assembly.⁠[1] Gas pressure tests, tube work and pilot cleaning are for a pro. A. O. Smith says supply problems may need a professional.⁠[5]

Still not fixed? Next likely cause: Weak or loose thermocouple

Thermocouple problems

The thermocouple (a thermopile on some models) is a heat sensor in the pilot flame. A. O. Smith explains that it powers the gas valve's pilot safety. If it breaks, the valve gets no power and the pilot dies when you release the knob.⁠[1] Bradford White's chart lists a loose connection at the gas control, a sensor not fully seated in the pilot bracket, a flame that doesn't fully cover its tip, and a weak sensor.⁠[3]

  1. Turn the gas control knob to off

    • Time: 2 min

    Use the lighting label's "to turn off gas" steps.⁠[1]

    You'll know it worked when: The heater is off and the pilot is out.

  2. Write down what you saw

    • Time: 5 min

    Note whether it went out on release or later, and copy the model and serial numbers from the rating plate.⁠[4]

    You'll know it worked when: You can tell the pro when the pilot went out and how often.

  3. Book a gas professional

    • Time: 5 min

    NFPA says a pilot that keeps going out should be relit by a fuel gas professional.⁠[2]

    You'll know it worked when: A qualified pro will test the thermocouple and gas valve.

The thermocouple sits in the gas burner assembly. Testing and fitting it means working on gas connections, so leave it to the pro.⁠[3]

Still not fixed? Next likely cause: Vent problem or downdraft

Vent problems and downdrafts

Exhaust from the burner rises through the flue and leaves through the vent. Bradford White lists a wrong, clogged or badly placed vent among the causes of a pilot that goes out now and then.⁠[3] A. O. Smith's manual says to shut the heater off at once and call a service agency when there are vent gas odors, a downdraft or poor combustion.⁠[4]

  1. Look at the vent pipe without touching it

    • Time: 5 min
    • LED work flashlight

    A. O. Smith's manual asks for a yearly look at the vent for blockages, damage and soot.⁠[4]

    You'll know it worked when: You know if the vent looks loose, rusted, sooty or blocked.

  2. Turn the gas off at the shutoff valve

    • Time: 2 min

    Do this if you see soot, smell exhaust or find the vent off its fitting. Leave if you smell gas.⁠[2]

    You'll know it worked when: The heater can't fire while the vent is in doubt.

  3. Call the gas utility or a gas pro

    • Time: 5 min

    A. O. Smith's manual says to call the local gas utility if you find soot or damage, and to have the vent cleaned or fixed before the heater runs again.⁠[4]

    You'll know it worked when: A pro is booked to inspect the vent before the heater runs again.

Vent work is never a DIY job. NFPA says to check that appliance vents let flue gases flow outside, and to have a fuel gas professional service gas appliances.⁠[2]

Still not fixed? Next likely cause: Faulty gas control valve

Gas control valve failure

The gas control valve holds the pilot safety parts. Bradford White's chart lists an open safety cutoff (ECO) and a faulty magnet inside the valve; both mean a new gas control.⁠[3] A. O. Smith says a failed control valve needs a service visit and most likely a new valve.⁠[1]

  1. Turn the gas off at the shutoff valve

    • Time: 2 min

    Only if you are confident doing so. If you smell gas, leave and call from outside.⁠[2]

    You'll know it worked when: No gas reaches the heater.

  2. Call a plumber or gas pro for a valve diagnosis

    • Time: 5 min

    A. O. Smith says a faulty gas valve should be inspected and replaced by a professional.⁠[5]

    You'll know it worked when: A qualified pro is booked with the model and serial numbers.

A new gas valve is a big repair on an older tank. Before you approve the work, find the water heater age from its serial number.

Still not fixed? See when to call a pro

When to call a pro

Call when the pilot goes out a second time, won't stay lit on release, or you smell gas or exhaust. NFPA says to contact a fuel gas professional to install, inspect, service and repair gas appliances.⁠[2]

Tell the pro when the pilot goes out. That one detail splits the thermocouple causes from the air and vent causes.⁠[3] If you also see water around the base, read about water heater leaks; water can damage gas controls.

Frequently asked questions

FAQ

Why does the pilot go out when I let go of the knob?
The flame sensor (thermocouple) is not holding the gas valve open. Bradford White lists a loose connection, a sensor out of the flame and a weak sensor as causes, and all need a pro.⁠[3]
Is it dangerous when the pilot keeps going out?
A pilot that goes out is usually safe because the valve shuts the gas off.⁠[1] But NFPA says a pilot that goes out again and again may signal a safety problem, so have a fuel gas professional check it.⁠[2]
How long should I wait before I relight the pilot?
At least 10 minutes with the gas control off, as A. O. Smith says. On models with a status light, wait until the light goes out.⁠[1]⁠[3]
Can I replace the thermocouple myself?
This guide does not cover it. The part sits in the gas burner assembly, and Bradford White's service manual is written for qualified service providers only.⁠[3]

Sources

  1. A. O. Smith · Manufacturer support

    “How To Relight A Water Heater's Pilot Light” · accessed

  2. National Fire Protection Association · Safety org

    “NFPA Educational Messages Desk Reference, 2026 Edition” · PDF · §19.3.1, §19.4.1, §19.4.2, §19.7.2 · accessed

  3. Bradford White · Manufacturer manual

    “Service Manual: Atmospheric Gas Water Heaters, Troubleshooting Guide and Instructions for Service (238-46647-00B)” · PDF · Cover; troubleshooting charts pp. 3-5; thermocouple testing p. 6 · accessed

  4. A. O. Smith · Manufacturer manual

    “Instruction Manual: Residential Gas Water Heaters, Power Vented Gas Models With Hot Surface Ignition (100341945)” · PDF · pp. 37, 40-41 (troubleshooting, vent system maintenance, housekeeping) · accessed

  5. A. O. Smith · Manufacturer support

    “Is Your Hot Water Not Getting Hot? Common Causes & What To Do About Them” · accessed

  6. U.S. Department of Energy, Building America · Government

    “Strategy Guideline: Proper Water Heater Selection” · PDF · §1.4.1, p. 6 · accessed

  7. A. O. Smith · Manufacturer support

    “Why Is My Water Heater Leaking?” · accessed

  8. A. O. Smith · Manufacturer support

    “Technical Bulletin 51: Puddle on Floor” · accessed

  9. A. O. Smith · Manufacturer support

    “Technical Bulletin 52: Leaking Temperature & Pressure Relief Valve” · accessed

  10. American Water Works Association (Opflow), via Howard County, Md., Department of Public Works · Trade association

    “Water Heater Dip Tubes: Why All the Fuss?” · accessed

How this guide was made

This guide was drafted with AI assistance from the manufacturer and safety sources listed above, then checked against those sources in an AI-assisted review. No licensed technician reviewed it. Last reviewed . Our methodology

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