Gas Water Heater Pilot Won’t Stay Lit | Fix It Today

Cold showers and a tiny flame that keeps quitting are a headache. The good news: most causes are predictable, testable, and fixable with basic tools and a steady approach. This guide shows clear checks, safe steps, and when to call a pro. You’ll also learn the small maintenance tasks that keep the flame steady for the long haul.

Pilot Light Keeps Going Out On A Gas Water Heater — Causes And Fixes

When a pilot won’t hold, think of three buckets: the flame isn’t hot or steady enough, the safety sensor isn’t sending the right signal, or something in the controls/air path is shutting things down. Start with quick observations, then move to simple tests.

Quick Diagnosis Table

Use this map to zero in on the likely cause before you grab a wrench.

Symptom You See	Likely Cause	What To Check First
Pilot lights, holds a few seconds, then dies	Weak thermocouple/thermopile, loose connection	Sensor tip position in flame, tightness of connector, millivolt output
Pilot won’t light or is tiny/yellow	Clogged pilot orifice, low gas flow	Clean orifice, verify gas shutoff is open, check for kinks
Pilot lights but main burner never fires	Low sensor voltage, bad gas control	Measure millivolts, check status light codes, inspect wiring
Pilot goes out during laundry or strong draft	Blocked combustion intake, room under-ventilated, downdraft	Clean flame arrestor/filter, add make-up air, check vent path
Status light blinks error code	High-limit trip, sensor fault, lockout	Decode code on label/manual, cool down, reset per instructions

Safety First

Turn the gas control to OFF and let the burner area cool before any work. If you ever smell gas, stop, ventilate the area, and call your gas supplier. A carbon monoxide alarm is non-negotiable near sleeping areas; see the CPSC guidance on CO safety.

Step-By-Step Checks That Solve Most Cases

1) Confirm A Clean, Blue, Steady Flame

A healthy pilot is sharp and blue with a small yellow tip at most. If the flame is lazy, noisy, or drifting, it can’t heat the safety sensor well enough to keep gas flowing.

How To Fix

• Relight per the label. Watch the flame shape through the viewport.
• If weak, remove the pilot tube and clear the orifice with compressed air. Don’t poke with hard wire.
• Re-seat the pilot tube and snug the fitting; don’t over-torque.

2) Clean The Air Path And Flame Arrestor

Tank models with FVIR designs pull combustion air through a screen and flame arrestor under the burner. Dust and lint starve the flame and cause nuisance shutdowns. Brush and vacuum the screen and the arrestor slots; this quick task fixes many “won’t stay lit” complaints. See the official A. O. Smith flame arrestor cleaning bulletin for the method and tool style.

3) Position And Test The Thermocouple/Thermopile

The sensor tip must sit directly in the blue cone. A couple of millimeters off target can drop the signal. On standing-pilot models, a thermocouple generates roughly a few dozen millivolts; on many newer tanks a thermopile makes a higher output to run electronics.

How To Fix

• With gas OFF and cooled parts, loosen the bracket and center the tip in the flame. Re-tighten.
• Shut gas OFF, disconnect the sensor from the gas valve, and measure DC millivolts while the pilot burns. Compare to spec in your manual. Readings well below spec point to replacement.
• Inspect the lead for kinks or soot. Clean the tip with fine abrasive only if sooted.

4) Decode The Gas Control’s Status Light

That blinking LED is a built-in translator. Count the flashes, match them to the decal or manual, and you’ll know whether you’re facing a high-limit trip, low sensor signal, or another lockout. Many tanks use Honeywell or White-Rodgers controls with a quick-reference chart on the cover.

5) Verify Safe Venting And Room Air

Poor draft or a backdraft can push the flame off the sensor. Check for birds’ nests at the cap, crushed sections, or a vent that was bumped loose. If the heater shares space with a clothes dryer or tight room, add make-up air so the burner can breathe.

6) Check The Thermal Switch (Resettable ECO)

Some models include a small resettable switch near the burner pan. If tripped, the pilot won’t hold. Clear the intake screen, let the unit cool, then press the reset firmly. If it trips again, fix the root cause (blocked air, flue trouble) before another attempt.

Measured Targets And What “Good” Looks Like

Use this table to compare your readings and observations against common healthy ranges. Always default to the specs in your model’s manual.

Item	Healthy Reading/Look	Notes
Pilot flame	Blue, steady, hits sensor tip	No roaring or lifting; no drifting yellow
Thermocouple output	Dozens of mV DC (per model spec)	Low mV = weak flame or bad sensor
Thermopile output	Hundreds of mV DC (per model spec)	Powers board/valve; loose leads drop output
Air intake screen	Free of lint and dust	Vacuum and brush the arrestor slots
Status light	Steady normal flash pattern	Use code chart on the control/decal

Common Fixes In Detail

Clean The Pilot Orifice

Shut gas OFF. Remove the pilot tube at the control and at the pilot hood. Blow compressed air backward through the orifice. Reinstall, leak-check with soapy water after reassembly, then relight per the label. A clean orifice restores a sharp flame that can heat the sensor correctly.

Replace A Weak Thermocouple Or Thermopile

Match the part to your brand and burner assembly. Remove the burner assembly as a unit, thread out the old sensor, and set the new one to the same depth. Route leads cleanly and tighten the connection at the gas control snugly. Relight and verify a steady flame and strong reading.

Clear The Flame Arrestor And Filter

Lint and pet hair collect fast near floor level. Slide a flexible brush through the intake openings around the base. Vacuum debris as you pull the brush back. Repeat until the brush comes out clean. This simple task restores airflow and stops nuisance lockouts.

Reset After A High-Limit Trip

Let the tank cool. Press the reset on the thermal switch (if present). Find the cause before firing again: blocked intake, vent obstructions, or a burner screen packed with lint are common culprits.

Troubleshooting By Scenario

The Pilot Holds Only While I Press The Button

That points to a sensor signal that drops the instant you release the button. Reposition the tip deeper into the blue cone, then recheck output. If readings stay low, replace the sensor.

The Pilot Looks Good But The Main Burner Won’t Ignite

Measure sensor output at the gas control under flame. If the reading meets spec, decode the status light. If the control still won’t open the main valve, the control may be faulty. At this stage, bring in a licensed tech.

The Pilot Goes Out When The Dryer Runs

Starved combustion air or a strong draft is stealing the flame. Clean the intake, open a louver, or add a make-up air kit. Check venting for proper rise and secure joints.

Care And Maintenance That Prevents Flame Dropouts

Monthly: Dust Control

• Vacuum around the base and behind the heater.
• Wipe the intake screen with a damp cloth.
• Keep storage boxes off the base so air can flow.

Quarterly: Pilot And Burner Check

• Observe the pilot flame through the viewport.
• Fire the burner. Listen for smooth ignition.
• Glance at the status light pattern for normal operation.

Yearly: Full Inspection

• Brush and vacuum the arrestor and intake screen thoroughly.
• Inspect venting end-to-end for clear path and tight joints.
• Check for water leaks, corrosion, and proper relief valve operation.

Model-Specific Notes

Exact relight steps, sensor specs, and error codes vary by brand and control model. Cross-check with your use-and-care manual. Rheem, A. O. Smith, and Bradford White publish lighting procedures, code charts, and intake cleaning methods in their documents. Keep a copy near the tank for quick reference.

When To Stop And Call A Pro

• You smell gas or see bubbles during a leak check.
• The flame lifts or rolls out of the chamber.
• Error codes persist after cleaning and resets.
• The pilot won’t hold after sensor replacement and proper positioning.
• Vent tests show poor draft or spillage at the draft hood.

Final Checks Before You Close The Panel

• Verify a crisp blue pilot contacting the sensor tip.
• Confirm normal status light pattern per the decal.
• Run hot water to prove main burner ignition, steady flame, and clean shutdown.
• Reinstall the access door snugly to keep the air path correct.

Do these basics well and that tiny flame will stay steady. Keep dust off the intake, keep the pilot sharp, and watch the status light. A few minutes of care saves relights, saves gas, and keeps hot water ready every day.