When a hot water heater pilot light won’t light, check gas supply, thermocouple contact, airflow, and ignition steps before calling a technician.
What This Guide Delivers
You get a clear path to restore hot water without guesswork. Start with fast checks, then move to targeted fixes. Each step keeps safety front and center.
Hot Water Heater Pilot Light Won’t Light — Common Causes
Gas water heaters use a small flame to light the main burner. If that flame will not start, one of a handful of parts or conditions is usually at fault. The list below covers the usual suspects and the first move for each.
| Likely Cause | What To Check | First Move |
|---|---|---|
| Closed gas valve or air in line | Gas cock position, recent work on lines | Set valve inline with pipe; purge air per manual |
| Dirty pilot orifice | Soot, spider webs, dust on pilot tip | Brush and blow out debris with gentle air |
| Faulty thermocouple / thermopile | Probe alignment in flame, snug connection | Re-seat, then test and replace if readings are low |
| Weak spark or bad igniter | Click sound, spark at pilot hood | Clean electrode; replace igniter if no spark |
| Draft or lack of combustion air | Open doors, tight closets, blocked screens | Shield from drafts; clear vents and intake |
| Failed gas control valve | No pilot gas flow with knob held down | Confirm supply; replace control if verified bad |
| Flammable vapor sensor lockout | Status light code on control | Ventilate area; follow reset steps or call a pro |
| Wrong relight sequence | Skipped wait time, wrong knob position | Follow the exact relight steps for your model |
Safety First, Always
If you smell gas, hear hissing, or a fuel gas alarm sounds, leave the area at once and contact your utility from a safe spot. Do not light matches or flip switches. Ventilate only as you exit. Personal safety beats any quick fix.
Identify Your Ignition Type
Water heaters use one of two broad setups. Older units keep a standing pilot that burns nonstop. Many newer models use electronic ignition that fires the pilot only when needed. The steps below point you to the right track for each type.
Standing Pilot (Manual Or Piezo Spark)
- Find the control knob with OFF, PILOT, and ON.
- Turn to OFF and wait at least ten minutes. This clears unburned gas.
- Turn to PILOT. Hold the knob down to feed pilot gas.
- Ignite with the built-in spark or a long lighter while holding the knob.
- Keep holding for 30–60 seconds so the flame heats the sensor.
- Release the knob. If the pilot stays lit, rotate to ON.
Electronic Ignition (Hot-Surface Or Spark Pilot)
- Cycle power per the manual to start the ignition sequence.
- Watch and listen near the sight glass for spark or glow.
- If the pilot fails after several tries, stop and let the unit sit ten minutes. Then move to checks below.
Step-By-Step Checks That Solve Most No-Light Cases
1) Confirm Gas Supply
Set the gas shutoff inline with the pipe. If a new installation or recent service introduced air, the pilot feed may sputter. Multiple relight tries with rests in between may be needed to purge small pockets of air. If lines were opened for longer work, a licensed tech should purge them.
2) Clean And Aim The Pilot
Dust and tiny cobwebs choke flow at the pilot orifice. Remove the burner door and lift the pilot hood. A soft brush and a short burst of compressed air clear the tip. Do not poke the hole with hard wire. When relit, the flame should be sharp and mostly blue with a small yellow tip touching the sensor.
3) Seat And Test The Thermocouple Or Thermopile
The flame sensor keeps gas flowing only when it feels heat. If the tip sits outside the flame, or the connector is loose, the pilot drops out as soon as you release the knob. Re-aim the probe so the top third sits in the flame. Snug the connector at the control body. If you have a meter, check output against the spec in your manual.
4) Restore Airflow
Water heaters need clean intake air and a clear draft path. Clear boxes from a tight closet, wash the intake screen, and check the vent for nests. A strong cross-breeze near the burner can also snuff a small flame. Reduce drafts during lighting.
5) Check The Igniter
With a sight glass view, press the spark button and watch. No spark, no click, or a cracked electrode points to a faulty igniter. Replace the module or electrode kit that matches your model.
6) Read The Status Light
Many controls flash a code that points to the fault. Count the blinks, then match them to the label on the heater or the manual. Codes often flag sensor faults, lockouts, or weak flame signals.
7) Suspect The Gas Control Only Last
The control is rugged and not the first thing to blame. If the pilot gets gas and burns strong but the control will not hold, or no pilot gas flows at all with the knob pressed, a failed control is possible. Replace only after all earlier steps pass.
Model-Specific Details That Matter
Relight steps and parts vary by brand and era. For A. O. Smith models, the official pilot relight and safety guidance lays out wait times, airflow needs, and the exact sequence. Use the sticker on your heater to pull the matching manual online.
Draft, Venting, And Combustion Air
Rooms with tight doors, sealed closets, or recent remodels can starve the flame. So can a lint-packed screen on flame-arrestor designs. Open the space, clear screens, and verify the vent path is open.
Thermocouple Versus Thermopile
Standing-pilot tanks often use a thermocouple. Many electronic controls use a thermopile that makes a stronger millivolt signal. Both prove flame and shut off gas if the flame goes out. Aligning the tip in the flame and keeping connections clean helps both styles do their job.
When To Stop And Call A Pro
Stop at once if you smell gas or see scorch marks, melted wire, or a buckled door. Stop if the pilot lights only with the door open, or if the flame lifts off the tip. Call a licensed tech for a full check when parts test bad or codes repeat after resets.
DIY Versus Pro: Smart Boundaries
Plenty of owners can clean a pilot, reseat a sensor, and follow the relight steps. Work on gas valves, sealed combustion parts, or vent repairs calls for training and permits in many areas. A short service visit often costs less than a wrong part and repeat no-hot-water days.
| Scenario | DIY? | Reason |
|---|---|---|
| Clean pilot orifice and re-aim sensor | Yes | Low risk with power and gas off |
| Replace igniter or electrode | Maybe | Simple parts swap on many models |
| Purge long gas lines | No | Needs licensed tools and leak checks |
| Replace gas control valve | No | Gas tightness and code checks required |
| Vent repair or re-route | No | Draft performance and fire codes apply |
| Diagnose repeated lockouts | Maybe | Read codes, then decide based on findings |
Parts, Tools, And Prep
Tools That Help
- Phillips and flat screwdrivers
- Adjustable wrench and small open-end set
- Soft brush and shop air or canned air
- Long lighter for manual pilots
- Multimeter that reads millivolts
- Flashlight and a small mirror
Prep Steps Before Any Work
- Turn the control to OFF and wait ten minutes.
- Shut off electric power to power-vent or electronic models.
- Close the cold water inlet if you will remove the burner door.
- Have fresh air in the room; prop a door if the space is tight.
Step-By-Step: Clean The Pilot And Sensor
- Remove the burner door and set screws aside in a cup.
- Lift the pilot hood and inspect the orifice.
- Brush away dust and webbing. Give one short air burst.
- Wipe the thermocouple or thermopile tip with a clean pad.
- Reinstall parts and route wires and tubes as they were.
- Relight. Watch the flame shape and confirm the sensor sits in it.
What A Healthy Pilot Flame Looks Like
A healthy flame is steady, blue, and firm, with a small yellow tip. It should wrap the top third of the sensor tip without lifting off. A lazy, mostly yellow flame hints at a clogged orifice or poor air mix. A tiny, wavering flame points to weak flow or drafts.
Link Out To Authoritative Guidance
For brand procedures and safety waits, see the A. O. Smith guide to relighting a pilot light
(official relight steps). For gas leak response, review NFPA’s list of actions for suspected leaks
(leave, call, and stay clear).
Keep It Running
Once the pilot lights and stays on, plan quick care once a season. Vacuum dust around the burner area. Rinse the intake screen. Check that storage boxes do not crowd the heater. Scan the vent from end to end. Small, steady care keeps the flame strong.
Quick Troubleshooting Flow
Start
Smell gas or hear hissing? Leave and call the utility. If clear, go on.
Then
Confirm gas valve position. Follow the relight steps for your model. No spark or flame? Clean the pilot and re-aim the sensor. Still no light? Test the sensor and check airflow. Repeat short relight tries with rests if air may be in lines. Codes or dead control? Book service.
Bottom Line
Most no-light issues trace to airflow, a dirty pilot, or a mis-seated sensor. Clean, re-aim, and follow the exact relight sequence. When safety warns or parts fail tests, let a licensed tech take it from there.