THE SHORT VERSION
- Smell gas? Don’t light anything. Leave, and call the gas company or 911 from outside.
- No gas smell: relight by the label on your tank. Turn the knob to OFF and wait (5 minutes on Rheem labels, 10 on A.O. Smith), set it to PILOT, push it in and click the igniter, then keep holding until the status light blinks or, on older Rheem controls, about 1 minute after the pilot lights.
- Won’t light at all: usually no gas to the heater, the knob not pushed fully in, an igniter that doesn’t spark, or a clogged pilot. Check the gas, then call.
- Lights, then goes out when you let go: usually the thermocouple or thermopile, a weak or misdirected pilot flame, or a safety shutoff. All of these are technician repairs. A thermocouple is about a $12 part; Fixr puts the installed price at $150–$325.
- Newer heaters talk: a blinking status light on the gas control gives a code. Two blinks usually means a weak pilot signal; four means the water overheated. Never open the sealed inner door to light the pilot by hand.
Before you relight: two checks that override everything else
Every gas water heater label starts the same way: before lighting, smell all around the heater, including next to the floor, because some gas is heavier than air (A.O. Smith and Rheem labels). If you smell gas, don’t light anything, don’t touch light switches and don’t use a phone in the house. Leave and call the gas company from outside. The full routine is in water heater emergency.
Second, don’t relight a heater that has been under water; the manufacturers say a flooded heater must be replaced. The same goes for one that may have ignited flammable vapors such as gasoline or solvent fumes. A.O. Smith says those heaters show discoloration on the air intake grid and must be replaced.
How a standing pilot keeps the gas on
Most gas tank water heaters have a standing pilot: a small flame that burns all the time and lights the main burner when the water needs heat. The gas control on the front of the tank lets gas flow only while a heat sensor in the pilot flame proves the pilot is burning. Rheem describes it as a safety device that shuts off the gas if the pilot goes out for any reason.
- Thermocouple
- A metal rod whose tip sits in the pilot flame and turns heat into a tiny voltage. That powers a safety magnet in the gas control, which holds the gas valve open. Bradford White’s service manual calls 20–30 millivolts good output on its test.
- Thermopile
- A bundle of thermocouples that makes much more power: 350–850 millivolts in Bradford White’s test. It powers electronic gas controls with a status light, such as Bradford White’s ICON system, with no house wiring.
- Piezo igniter
- The push button beside the knob. Each press makes a spark at the pilot.
Why you can’t light it with a match anymore
In 2003 the Consumer Product Safety Commission (CPSC) estimated that gas water heaters igniting gasoline and other vapors were involved in nearly 800 home fires a year. An industry standard then made tank-type gas heaters built after July 1, 2003 flammable vapor ignition resistant (FVIR). The burner sits in a sealed chamber, and air comes in only through a flame arrestor, a perforated plate that lets vapors burn inside but stops the flame from reaching the room. A heat-sensing switch (Bradford White) or combustion shutoff device (Rheem) then stops the pilot and burner. The same switch trips if lint, dust or oil clog the arrestor.
That’s why the inner door stays shut. Rheem seals the chamber with a gasket and tamper-resistant screws, and Bradford White warns that with the inner door off, its vapor protection is switched off.
How to relight the pilot, step by step
Follow the lighting label on your own heater, usually on the front near the gas control. Wait and hold times differ by manufacturer. This is the common sequence:
Turn the knob to OFF and wait
Turn the gas control knob to OFF. Some controls need a slight push to get past PILOT; don’t force it. Wait 5 minutes (Rheem) or 10 minutes (A.O. Smith) for gas to clear.
Smell for gas again
If you smell gas now, stop and leave.
Take off the outer cover only
Remove the outer burner cover so you can see the sight glass, the small window in the inner door. Leave the inner door alone.
Set the knob to PILOT and push it all the way in
A.O. Smith says the knob travels in about 1/4 inch when it’s set correctly.
Click the igniter while holding the knob in
A.O. Smith says about once a second, for up to 90 seconds. Watch through the sight glass for the flame.
Keep holding
The sensor must heat up before it can hold the valve open. With a status light, hold until it blinks (up to 90 seconds on A.O. Smith and Rheem controls). Rheem’s older mechanical label says about 1 minute after the pilot lights.
Release, set the temperature, replace the cover
The knob should pop back out; Rheem says if it doesn’t, stop and call. Set your temperature and replace the cover.
| Label | Wait after OFF | Hold the knob | Give up when |
|---|---|---|---|
| A.O. Smith Signature 100 (status light) | 10 minutes | Until the status light blinks, up to 90 seconds | 3 attempts, 10 minutes apart; then OFF and call |
| Rheem, electronic control (status light) | 5 minutes | Until the status light blinks; if no blink and no flame after 90 seconds, start over | Several attempts; then OFF and call |
| Rheem, mechanical control (thermocouple) | 5 minutes | About 1 minute after the pilot lights | Several tries, or the knob won’t pop back out |
Sources: A.O. Smith manual 100341468 (2021); Rheem Use & Care manuals AP16801-2 (2014) and AP14328-7, both linked from a current Rheem model’s Home Depot page. Your label may differ; follow it.
What a healthy pilot flame looks like
Resideo, which makes replacement pilot burners, says a good pilot flame is blue, soft and steady and wraps the top 3/8 to 1/2 inch of the thermocouple or thermopile tip; a yellow tip is acceptable on propane. Bradford White and A.O. Smith both list a flame that doesn’t reach the sensor as a cause of outages. Rheem suggests a yearly look through the sight glass, and shutting the heater off if anything looks unusual.
When the pilot won’t light at all
You click and click, and no flame appears in the sight glass. The manuals list these causes:
- No gas to the heater. If the stove or furnace won’t light either, the gas is off upstream: an outage, a shut-off meter or an empty propane tank. Call the utility or propane supplier; don’t turn a meter back on yourself. See no hot water.
- Knob not at PILOT or not pushed fully in. Bradford White and Rheem both list it. Recheck the label.
- No spark. Watch the sight glass while clicking. No spark points to the igniter or its wire, both replaceable parts.
- Air in the gas line, usually after gas work. Rheem says a technician should purge it.
- A clogged pilot orifice or pinched pilot tube. On some electronic pilots the whole pilot assembly is replaced (Bradford White).
- A tripped safety shutoff, covered below.
When it lights but won’t stay lit
Either the pilot dies the moment you let go of the knob, or it runs for hours or days and then goes out.
Goes out when you release the knob
- Weak or failed thermocouple or thermopile. It’s on every manufacturer’s list, and a technician replaces it.
- Loose connection or misplaced sensor. Bradford White lists a loose thermocouple nut and a sensor not seated in its bracket; A.O. Smith, a thermopile tip not in the flame.
- A small or dirty pilot flame that doesn’t wrap the tip, from a dirty pilot, a clogged orifice or low gas pressure.
- You didn’t hold long enough. The one cause you can fix: hold for the full time on the label.
- A failed gas control, such as a worn safety magnet or a high-temperature cutoff that has opened. The fix is a new gas control.
Goes out now and then
- Not enough combustion air, Bradford White’s first cause. A.O. Smith tells owners to vacuum dust and lint around the base; Rheem wants at least 1 inch of clearance at the inlets in a closet.
- Draft or backdraft. Bradford White lists a wrong or clogged vent, and Resideo says a waving flame points to draft or exhaust being pulled back. Melted plastic rings on the pipes or soot on the tank top are backdraft signs (Pacific Northwest National Laboratory). See water heater venting.
- An unsteady gas supply (Bradford White).
- Condensation dripping down the flue onto the burner, mostly with very cold incoming water or an undersized tank (A.O. Smith).
A safety switch has tripped
FVIR heaters shut down when they sense vapors burning in the chamber or too little air. Bradford White’s switch has a red reset button on the inner door, and A.O. Smith’s chart includes pressing a reset button behind the outer door. But Bradford White and Rheem treat a trip as a reason to find the cause: vapors, lint on the arrestor or starved air. Cleaning the arrestor means taking the burner out, which is technician work.
What the blinking status light means
Gas controls powered by a thermopile have an LED that blinks in patterns, with a pause of about 3 seconds between them. Meanings vary by brand and valve maker; Bradford White alone has separate charts for Honeywell and White-Rodgers controls. Use the chart on your heater or in its manual. Three examples:
| Blinks | A.O. Smith | Rheem | Bradford White (Honeywell V2) |
|---|---|---|---|
| None | Pilot out, or thermopile still warming up | Control off or pilot out | No power from the pilot; light it |
| Solid on | Pilot just went out; thermopile cooling. Wait 10 minutes | Pilot recently out or knob just turned off | Control is off; wait until the light goes out |
| 1 | Normal (one blink every 3 seconds) | Normal (one blue blink every 3 seconds) | Normal, green (every 4 seconds: pilot only; every second: burner on) |
| 2 | Pilot lit, thermopile output too low | Thermopile voltage low | Low thermopile voltage (yellow); check pilot flame |
| 4 | Water got too hot; gas control replaced | High-temperature shutdown | Temperature limit reached |
| 5 | Temperature sensor failed | Temperature sensor failure | Electronics or sensor fault |
| 7 | Gas control failure | Gas control failure | — |
| 8 | Pilot still burning with knob off (stuck valve) | False pilot flame signal | — |
Sources: A.O. Smith manual 100341468 (2021), Table 5; Rheem manual AP16801-2, status light chart; Bradford White service manual 238-51542-00C (2019), Honeywell V2 chart. A dash means the code isn’t in that chart.
Two blinks is the classic pilot code: the pilot is lit but not heating the sensor enough, from a failing thermopile, loose wiring, an unstable pilot or a blocked pilot tube (Bradford White). Four blinks means the water overheated. A.O. Smith calls its shutoff non-resettable and replaces the gas control; Bradford White’s Honeywell and White-Rodgers controls reset after 5 minutes at OFF. Either way, turn the knob to OFF and call.
Power-vent and electronic-ignition heaters have no pilot
A heater with a fan on top and a power cord probably has no pilot. A.O. Smith and Rheem power-vent labels say so plainly: “This appliance does not have a pilot.” A hot surface igniter lights the burner each time the water needs heat. After three failed tries, the control locks out and flashes a code.
- Check the plug, the outlet and the ON/OFF switch on the blower.
- A.O. Smith’s reset for a soft lockout: switch OFF, wait 10 seconds, switch ON. It locks out again if the cause remains.
- A pressure switch shuts the heater down if the vent is blocked (A.O. Smith). Check that snow or debris isn’t covering the outside end, but don’t take vent pipes apart.
More in no hot water and, for tankless units, tankless error codes.
Troubleshooting table: symptom, cause, safe check, when to call
| What you see | Likely cause | What you can safely check | Call when |
|---|---|---|---|
| Gas smell anywhere | Gas leak | Nothing. Leave the house | Now, from outside |
| Pilot out, no other symptoms | Draft, brief gas interruption | Relight by the label | It goes out again soon |
| No flame, no spark in the sight glass | Igniter or its wire | Click while watching the sight glass | Still no spark |
| Spark, but no flame | Gas off, air in line, clogged pilot | Other gas appliances work? Knob fully in? | Gas is on and it still won’t light in 3 tries |
| Lights, dies when you let go | Thermocouple or thermopile, flame not on tip, gas control | Hold the full time on the label | It dies a second time |
| Small, yellow or wavering flame | Dirty or clogged pilot, low pressure, draft | Look only; clear lint around the base | Always; it needs cleaning or adjusting |
| Goes out every few days | Combustion air, vent, gas supply, condensation | Air inlets clear; no melted plastic or soot on top | It keeps happening, or you see backdraft signs |
| Won’t light; reset button on inner door popped | Thermal switch tripped | Remove solvents, ventilate | Before any reset if you smelled fumes; after one trip otherwise |
| Status light: 4 blinks | Water overheated | Knob to OFF | Right away |
| Power-vent heater, code flashing | Lockout, blocked vent, vapor sensor | Power, switch, outside vent; one reset | Code returns |
Sources: A.O. Smith (2021, 2023), Rheem (2014, 2017) and Bradford White (2019) manuals; Resideo pilot burner instructions. Your heater’s label and manual come first.
Repair or replace: what pilot fixes cost
Almost every pilot problem is a replaceable part on a sound tank, and most of the bill is the visit and labor:
| Job | Part at Home Depot | HomeAdvisor | Fixr |
|---|---|---|---|
| Service call to diagnose and relight | none | $50–$150 | $75–$175 (pilot light repair) |
| Replace thermocouple | about $12 | about $150 | $150–$325 |
| Replace gas control valve | varies by model | about $350 | not listed |
HomeAdvisor water heater repair cost guide (updated June 2026) and Fixr water heater repair cost guide (updated August 2025); both are lead-generation sites, not measured local prices. Part: Everbilt 24 in. thermocouple, homedepot.com, October 4, 2026. Thermopiles and pilot assemblies are model-specific.
Repair is the normal answer. Replace instead if the heater was flooded or went through a vapor ignition (manufacturers require it), if the tank leaks, or if an expensive part like the gas control fails on an old tank. Rheem puts typical tank life at 8–12 years. The serial number tells you the age (how old is my water heater); repair or replace has the math.
Tell the technician
- Brand, model and serial number from the rating plate
- The status light pattern, counted exactly
- Whether it won’t light, or lights and then goes out (and how long it stays lit)
- What the flame looked like, and whether you saw a spark
- Any recent gas work, propane refill, flooding, or solvent or gasoline use nearby
Common questions
How long do you hold the pilot button on a water heater?
As long as your label says. A.O. Smith and Rheem controls with a status light: hold until the light starts blinking, up to 90 seconds. Rheem’s older mechanical control: about 1 minute after the pilot lights. The sensor has to heat up before it can hold the gas valve open.
Why does my water heater pilot light keep going out?
If it goes out the moment you release the knob, the usual cause is a weak thermocouple or thermopile, or a flame that doesn’t reach it. If it goes out every few days, Bradford White points to combustion air, the vent or the gas supply, and A.O. Smith adds condensation dripping onto the burner. Both need a technician to diagnose.
Can I light my water heater pilot with a lighter or match?
Not on flammable vapor resistant (FVIR) heaters, the standard for tank models built since mid-2003. They have sealed combustion chambers, and A.O. Smith and Rheem labels say never to open the inner door and light the pilot by hand. Use the built-in igniter. If it doesn’t spark, the igniter needs replacing.
How much does it cost to replace a water heater thermocouple?
Fixr lists $150–$325 installed and HomeAdvisor about $150, while the part itself is about $12 at Home Depot. Most newer heaters use a thermopile or a pilot assembly specific to the model instead, so get the price for your model.
Is it safe to relight a water heater pilot myself?
Yes, if you don’t smell gas and you follow the label on the heater exactly. Stop after three tries (A.O. Smith’s limit) or if the knob sticks. Don’t relight if the heater was flooded or may have ignited vapors.
My water heater light is blinking twice. What does that mean?
On A.O. Smith, Rheem and Bradford White charts, two blinks means the pilot is lit but the thermopile isn’t making enough power. That usually means a weak thermopile, a loose connection or a weak pilot flame, and it needs a technician.
Why do I have to wait 10 minutes between lighting attempts?
To let unburned gas clear, and on some controls to let the electronics reset. A.O. Smith says its valve’s circuitry requires the 10-minute wait. Rheem’s labels use 5 minutes. A solid status light means the thermopile is still cooling; wait for it to go out.
Sources
Sources checked October 4, 2026. Prices, codes and rebates change. Check current details with your installer and local permit office.
- Signature 100 gas water heater installation instructions and use & care guide 100341468 (2021) ↗ · A.O. Smith
- Use & care manual AP16801-2, residential gas FVIR water heaters with electronic control (2014) ↗ · Rheem, hosted by Home Depot
- Use & care manual AP14328-7, residential gas FVIR water heaters (mechanical control) ↗ · Rheem, hosted by Home Depot
- Service manual 238-51542-00C, Defender FVIR gas water heaters (2019) ↗ · Bradford White, hosted by G.T. Sanders
- Residential atmospheric vent gas water heaters spec sheet (ICON system) ↗ · Bradford White, hosted by Young Supply
- Q314 and Q327A pilot burners installation instructions 69-0519 (2020) ↗ · Resideo
- New technology in gas water heaters can save lives (release 03-158, 2003) ↗ · U.S. Consumer Product Safety Commission
- Installation instructions and use & care guide, power-vent gas water heaters 100366722 (2023) ↗ · A.O. Smith, hosted by Lowe’s
- Low NOx power-vent gas water heater use & care manual AP16412-1 (2017) ↗ · Rheem, hosted by InspectAPedia
- Look for signs of gas water heater backdrafting ↗ · Pacific Northwest National Laboratory, Building America Solution Center
- Water heater repair cost (updated June 2026) ↗ · HomeAdvisor
- Water heater repair cost (updated August 2025) ↗ · Fixr
- Everbilt 24 in. gas water heater thermocouple EBTC-24 (product page) ↗ · Home Depot
- Water heater lifespan: when to repair vs. replace ↗ · Rheem