When a gas water heater doesn’t light, check gas supply, ignition spark, airflow, and safety sensors before calling a pro.
Cold shower. Clicking igniter. No flame. You can fix many no-light problems in minutes with a calm, methodical check. This guide walks through quick wins first, then deeper steps—always with safety in mind.
Safety First Before Any Checks
If you smell gas, hear hissing, or see soot around the burner door, stop. Leave the area and contact your gas utility or 911 from a safe spot. Utilities give clear steps on what to do when you smell gas; see guidance from a public utility regulator’s gas-leak page. Work only when the area is odor-free and well-ventilated.
When The Water Heater Doesn’t Light: Quick Checks
Work through these in order. Each step either restores flame or points to the next check.
- Gas shutoff position: The handle should be parallel to the pipe. If perpendicular, gas is off. Turn parallel and wait a minute for pressure to equalize.
- Appliance control at “Pilot” or “Ignite”: Set the knob correctly per the lighting label on the tank. Hold the pilot button as directed.
- Spark check: Press the igniter. Look through the sight glass for a blue spark at the pilot tip. No spark? The piezo wire or igniter may be loose or failed.
- Pilot flame quality: A steady blue flame should wrap the thermocouple/thermopile tip. A weak, yellow-tipped flame can’t heat the sensor.
- Drafts and airflow: Remove debris around the base or flame arrestor screen. Strong drafts at the burner door can snuff a small flame.
- Wait time: On first light after shutdown or bottle swap, air may be in the line. Hold the pilot button down and spark several times; give it 30–60 seconds.
Common Symptoms And Likely Causes
Use this broad map to match what you see with a likely cause and a quick test.
| Symptom | Likely Cause | Quick Check |
|---|---|---|
| Spark but no flame | No gas at pilot, clogged pilot orifice | Confirm gas valve on; try bleeding air; inspect pilot tube/orifice |
| Pilot lights, won’t stay lit | Weak thermocouple/thermopile, flame not hitting sensor | Check flame shape; reseat or replace sensor |
| No spark at all | Bad igniter, loose wire, cracked electrode | Verify click; inspect lead and ceramic insulator |
| Frequent blow-outs | Drafts, blocked air screen, venting issue | Clean base screen; shield from drafts; inspect vent |
| Clicks, brief flame, burner never follows | Thermal cutoff tripped, ECO fault, gas valve issue | Let unit cool; reset per label; inspect wiring |
| After tank flush, no light | Air in line, wet pilot area | Dry components; repeat lighting with longer hold |
How The Pilot System Keeps Flame On
The small pilot heats a sensor. On many tanks, that sensor is a thermocouple (older style) or a thermopile (produces more millivolts). When hot, the sensor feeds millivolts to the gas valve coil so the valve stays open. If the pilot cools, the valve shuts to keep gas from flowing. A weak flame or a dirty sensor breaks this chain.
Fixes You Can Do In Minutes
Confirm Gas Flow To The Appliance
Set other gas appliances to run for a moment. If they work, gas service is present. If none run, call your gas provider. If only the heater fails, the issue sits at the appliance.
Reseat Or Replace The Sensor
A loose thermocouple won’t pass enough heat or signal. Hand-tighten the nut at the gas valve, then give a small wrench snug. Do not overtighten. If the tip is sooty or bent, replace it with the correct kit for your model. A thermopile usually plugs into a two-wire connector on modern valves; match the part number for your heater.
Clean The Pilot Orifice And Tube
Shut gas off. Remove the pilot tube from the valve and the burner assembly. A tiny spider web or dust can clog the orifice. Use compressed air or a fine wire from the pilot side out to avoid pushing debris deeper. Reassemble, leak-check with soapy water, and relight.
Restore Air To The Burner
Many modern tanks breathe through a flame-arrestor screen at the base. Lint and dust can choke it. Brush the screen clean or vacuum gently. Clear cardboard, pet hair, and storage items from around the base so the heater can draw air freely.
Check The Spark Path
Press the igniter while watching the sight glass. No spark? Pull the igniter lead and reseat it. Look for cracked ceramic on the electrode. If the lead is frayed or the button never clicks, swap the igniter kit. Some makers provide a simple diagnostic flow for this step; see a brand support page such as A. O. Smith’s pilot help for a typical spark-test sequence: pilot does not light.
Deeper Causes And Solid Fix Paths
Weak Thermocouple/Thermopile
A sensor that no longer makes enough millivolts won’t hold the pilot on. A strong pilot should wrap the tip in blue flame. If the flame is fine, test the sensor with a multimeter (thermocouple in millivolts DC; thermopile often reads a few hundred millivolts). If readings are low, replace the part with an OEM kit.
Dirty Burner Or Misplaced Pilot
If the main burner whooshes on and blows the pilot out, the flame may lift from the ports due to dust or poor air mix. Remove the burner assembly, brush ports, and reinstall so the pilot points into the burner stream as designed.
Vent Or Draft Problems
Backdrafts push fumes toward the pilot. Check the vent connector for dips, loose joints, or bird nests at the cap. The connector should rise off the draft hood and run uphill to the chimney with minimal elbows. If the vent is shared with a furnace, both appliances need correct sizing and clear pathways.
Sediment And Overheat Cutoffs
Heavy sediment can make the base of the tank run hot. Some heaters include an ECO (energy cut-off) that trips under high temperature at the base. If your model lists an ECO trip in the lighting label, follow the reset steps only after the unit cools. To limit sediment, periodic draining and a brief flush help; the U.S. Department of Energy lists tank care tasks such as periodic flushing, T&P valve checks, and anode inspection on its storage water heaters page.
Gas Valve Faults
If a healthy pilot and sensor still can’t bring the main burner on, the gas control may have failed internally. Confirm sensor output, confirm call for heat, and verify no lockout codes. At that point, a licensed tech can replace the valve and leak-check the joints.
Exact Steps To Relight Safely
Every tank includes a lighting label. Follow that first. Here’s a plain, model-agnostic sequence that mirrors most labels:
- Turn the control knob to “Off.” Wait five minutes for any gas to clear.
- Turn the knob to “Pilot.” Hold the pilot button down.
- Press the igniter repeatedly while holding the button. Watch for a small blue flame.
- Keep holding the button 30–60 seconds after the flame appears to heat the sensor.
- Release the button. If the flame stays, turn the knob to “On.” Set temperature to a safe mark (120–125°F is common for homes).
If the flame goes out on release, return to the sensor and pilot checks above.
Electric Units: If Yours Uses Elements, Not Burners
Some households have electric tanks. No flame there—only heating elements. If your water is cold, check the breaker, then the reset button on the upper thermostat. Burned elements or faulty thermostats are common. Power off at the breaker, remove the access covers, and test the elements with a multimeter. Replace weak parts with the same rating. Insulate the access covers tight after the repair.
Smart Prevention So You Rarely Face A No-Light
Keep Air And Flame Paths Clean
Vacuum around the base a few times a year, brush the flame-arrestor screen, and keep cardboard and storage bins away from the heater so it can breathe.
Flush Sediment Briefly
Drain a few quarts from the drain valve until water runs clear. This quick task reduces popping, cuts base overheating, and helps ignition stability during long burns. Many guides recommend a short flush rhythm through the year; a federal energy page on water heating lists routine maintenance steps and efficiency tips that pair well with this habit.
Check The Anode And T&P Valve
Swap the sacrificial anode when it’s eaten down. Test the temperature-and-pressure valve a couple of times a year so it moves freely. These two checks lengthen tank life and reduce stress on the burner cycle.
Model-Specific Clues To Watch
Modern gas controls often blink status codes. A repeating pattern might flag weak sensor output, ignition lockout, or high-temp trip. The lighting label or a QR link on the tank usually decodes the pattern. If your sticker is missing, a quick search of the model number on the maker’s site turns up the blink chart and part lists.
DIY Or Call A Tech?
Many fixes above are simple: open a gas shutoff, clean a pilot orifice, reseat a sensor, clear the base screen. Call a licensed pro when you see scorch marks, a melted wire, repeat lockouts, gas leaks, or venting defects. A tech can test draft with a smoke source, measure sensor output, verify manifold pressure, and swap a valve safely.
Parts, Lifespan, And When Replacement Wins
Burners and sensors are wear items. Tanks with age and heavy sediment can fight you with repeat ignition faults. Use the table below as a ballpark guide for timing and choices. Prices vary by brand and region.
| Part Or Task | Typical Interval | Notes |
|---|---|---|
| Thermocouple / Thermopile | 5–8 years | Replace if pilot won’t hold with strong flame |
| Pilot Assembly | 8–12 years | Swap when tube/orifice cleaning no longer helps |
| Gas Control Valve | 10+ years | Replace on confirmed internal fault, not guesswork |
| Sediment Flush | Quarterly–Annual | Short drain keeps base temps stable during burns |
| Anode Inspection | 3–4 years | Swap before the core steel shows |
| Tank Replacement | 10–12 years | Old, leaking, or repeated no-light faults may justify new |
Tankless Units: No Pilot, Still Needs Air And Clean Parts
Tankless heaters use electronic ignition, flow sensors, and tight air pathways. If yours clicks but fails to fire, check inlet screens, vent pipes, and condensate drains. Descale the heat exchanger per the manual. Many no-fire cases trace to low flow from clogged screens or a blocked vent. Use only the service valves installed for flushing.
Simple Toolkit For These Repairs
- Adjustable wrench and a small open-end set
- Phillips and flat screwdrivers
- Shop vacuum and soft brush
- Compressed air can or hand pump
- Spray bottle with dish soap and water for leak checks
- Multimeter with millivolt range for sensor tests
- Work gloves and eye protection
Leak Checks You Should Always Perform
Any time you loosen gas fittings, finish with a soap-and-water test on the joint while the gas is on. Watch for steady bubbles. If bubbles grow, shut gas off and refit the joint.
Vent And Combustion Air Rules Of Thumb
Keep the vent rising from the draft hood with minimal elbows. Replace rusted sections. Keep storage clear so the heater can draw air. A closet install usually needs louvered doors or dedicated air grilles sized per the manual.
When You’ve Fixed The Flame, Set It Up For A Smooth Run
After the burner fires, let it run and watch. The flame should be steady, mostly blue with small orange tips at the burner ports. No roaring, no lifting. Set temperature to a safe mark, check for hot water at a sink, then do a last pass for leaks and smells. Mark the next quick flush date on a piece of tape on the jacket so you keep the rhythm going.
Quick Recap You Can Screenshot
- Gas on, knob set, hold the pilot button long enough
- Blue flame wrapping the sensor, not flickering away
- Clean pilot orifice and base air screen
- Reseat or replace thermocouple/thermopile when weak
- Clear vent runs and stop drafts at the burner door
- Flush sediment, test T&P, check anode on a schedule