Heater Pilot Light Won’t Stay Lit | No-Nonsense Fixes

You light the flame, it looks steady, then it quits a minute later. That pattern wastes time and gas, and it leaves the room cold. This guide shows clear checks, safe cleaning steps, and when to call a pro. You’ll find quick wins up top, deeper fixes next, and a parts table with plain prices near the end.

When A Heater’s Pilot Flame Won’t Stay On: Quick Checks

Start with the basics. Each step builds on the last, so move in order. If you smell gas, stop and call your utility or a licensed tech.

Symptom	Likely Cause	What To Try
Flame lights but drops out in 10–60 seconds	Weak or misaligned thermocouple/thermopile	Re-seat tip in the flame; snug the nut a quarter turn; test or replace
Small, lazy, yellow flame	Clogged pilot orifice; dust in air path	Power down; clean the pilot tube/orifice; vacuum intake screens
Flame blows out when main burner starts	Draft or backdraft at the draft hood	Check vent rise, joint gaps, wind; keep doors closed; fix venting
Can’t light at all, no hiss	Closed gas cock or empty LP tank	Open the valve; verify LP level; relight per label
Clicks/sparks but no light	Air in gas line; weak spark; dirty electrode	Hold pilot button longer; purge; clean the igniter
Goes out overnight	Low inlet pressure or failing gas control	Have pressure checked; replace control if out of spec

Safety First Before You Touch Anything

Set the gas control to OFF and let the chamber cool. Work in a bright space with steady airflow, not a gusty garage bay. A carbon monoxide alarm should sit nearby any fuel burner in the home. The U.S. Consumer Product Safety Commission explains the risk and prevention steps in its Carbon Monoxide Information Center.

How The Flame-Proving Parts Work

The tiny flame heats a sensor. On older gear that sensor is a thermocouple; on some systems it’s a thermopile. Heat creates a small millivolt signal that keeps the gas valve’s safety circuit held in. If the signal falls, the valve snaps shut and the flame dies. That design keeps gas from flowing when there’s no flame.

Step-By-Step: Clean And Align The Pilot Assembly

1) Shut Down And Access The Burner

Turn gas control to OFF and close the service valve. Wait five minutes. Remove the burner door and pull the burner tray if the model allows. Snap a phone photo first so re-assembly is simple.

2) Clear The Pilot Orifice

Dust and lint choke the pilot stream, which weakens the flame. Do not poke with a toothpick or a drill bit. Use compressed air or a soft brush on the orifice and pilot tube. If the orifice looks damaged, replace it.

3) Clean The Sensor Tip

Wipe the thermocouple or thermopile tip with fine emery cloth. Only the soot comes off; don’t remove metal. Re-install so the tip sits in the upper third of the pilot flame. A blue cone touching the tip is the target.

4) Check The Connection

At the gas control, snug the thermocouple nut one quarter turn past finger tight. Do not crank it. A loose connection drops millivolts and the safety circuit opens.

5) Clean The Air Path

Vacuum the burner tray, intake louvers, and flame arrestor screens under tank-style water heaters. A dust mat starves the flame for air and makes it yellow and weak.

Draft And Vent Checks That Stop Blow-Outs

Stand near the draft hood with the flame lit. Hold a tissue strip near the hood; it should pull into the hood. If it pushes out, you likely have backdraft. Wind, a short vent rise, a plugged cap, or negative house pressure can all cause that. Fixing venting is a job for a licensed tech.

Many older systems use a standing flame. Upgrading to electronic ignition removes that always-on flame and improves fuel use. The U.S. Department of Energy notes that intermittent ignition devices cut fuel use a few percent on older boilers and furnaces; details appear on its page on gas-fired boilers and furnaces.

Relight Steps That Don’t Fight You

Label Directions Come First

Follow the lighting label on the unit. If the label is gone, use the brand manual for your exact model. Never guess at the sequence.

Hand-Lighting Sequence (Standing Flame)

1. Set the control to OFF. Wait five minutes.
2. Turn to PILOT. Press and hold the button.
3. Use the igniter or a long match to light the pilot.
4. Keep holding the button for 30–60 seconds so the sensor heats.
5. Release. If the flame holds, turn to ON and set the thermostat.

Spark-Ignited Sequence (Where Equipped)

1. Set to PILOT/IGNITE.
2. Press and hold as you press the spark button.
3. Once the flame lights, hold for 30–60 seconds, then switch to ON.

What Each Flame Color Tells You

• Steady Blue With A Small Yellow Tip: Normal. Sensor sits in the blue cone.
• Large Yellow Or Flicker: Dirt in the orifice or not enough air. Clean the orifice and intake.
• Flame Lifts Or Waves: Draft across the hood or door. Close doors, shield from wind, check vent cap.
• Green/Orange Specks: Dust or copper residue burning off. Clean and recheck.

Gas Supply Clues

Natural gas: a service issue or a half-closed valve can drop pressure. Propane: a low tank or a frozen regulator can starve the flame. If other gas appliances also seem weak, call the supplier. A licensed tech can set a manometer and read inlet and manifold pressure.

When Parts Fail And What They Cost

Small parts keep the safety chain alive. Here’s a ballpark list to plan a repair. Prices vary by brand and region.

Part	What It Does	Typical Price*
Thermocouple	Feeds a millivolt signal to hold the gas safety circuit	$10–$25
Thermopile	Multi-junction sensor that powers low-voltage circuits	$25–$60
Pilot Assembly	Nozzle, tube, sensor, and bracket as a set	$40–$120
Igniter/Electrode	Creates the spark to light the pilot	$15–$50
Gas Control Valve	Controls pilot and main burner flow	$120–$300+
Vent Cap	Keeps rain and pests out; sets draft	$20–$80

*Parts only. Labor varies.

Deeper Diagnostics That Save Repeat Calls

Millivolt Check

With a meter set to mV, read the thermocouple under pilot load. Many heaters need ~10–30 mV at the gas valve. If the reading is low even with a strong blue flame on the tip, swap the sensor.

Spill Test

With the main burner running, hold a smoke source at the draft hood edge. Smoke should pull in. If it spills out, shut the unit down and fix venting.

Combustion Air

Closets and small rooms starve burners. Add louvered doors or code-sized grilles. Keep storage away from the burner area so air can move.

Common Scenarios And Straightforward Fixes

The Flame Holds Only While You Press The Pilot Button

The sensor is cold, dirty, or misaligned. Clean the tip and keep holding the button for a full minute on relight. If it still drops out, replace the sensor.

The Flame Dies When The Main Burner Fires

The burner whoosh can knock a weak pilot off. Clean the orifice and set the sensor deeper into the blue cone. Check draft as well.

The Flame Returns For A Day Then Quits Again

That pattern points to a borderline sensor or low gas pressure. Replace the sensor and have a tech read pressure with a manometer.

Preventive Care That Keeps The Flame Steady

• Vacuum intake screens twice a year.
• Keep flammables far from the burner door.
• Replace worn door gaskets so room air flows as designed.
• Test carbon monoxide alarms monthly and replace units at end of life.
• Book yearly service for a draft test, gas-pressure read, and a full cleaning.

When To Stop And Call A Pro

Any smell of gas calls for an immediate shutdown and a call to the utility. If the flame stays yellow after cleaning, if draft fails the tissue test, or if the unit trips a spill switch, stop. Venting or gas-pressure work needs licensed tools and training.

Is An Upgrade Worth It?

Many older units use a constant flame. Newer models fire the pilot only when needed or use hot-surface ignition. That cuts fuel and ends pilot outages from dust or draft. The Energy Saver page on intermittent ignition devices gives a quick rundown along with other upgrade paths.

Your Action Plan

1. Clean the orifice, sensor tip, and air path.
2. Re-seat the sensor in the flame and snug the connection.
3. Verify steady draft at the hood.
4. Relight per the label and hold long enough to heat the sensor.
5. If the flame still drops, replace the sensor; then check gas pressure.
6. Book a pro for vent or gas-valve work, or plan an ignition upgrade.

Small Details That Trip People Up

Door position matters. A tight mechanical room with the door shut can pull the flame off the sensor when the main burner lights. Try a test with the door open, then add proper makeup air so the fix is permanent. Wind at the vent cap also matters. A missing bird screen or a dented cap lets gusts shove air down the pipe.

Thermostat calls can mislead. If the thermostat sends heat calls in short bursts, the pilot may never warm the sensor long enough to hold. Confirm cycle length and temperature swing, then test again. Last, look for corrosion at ground points. A loose or rusty ground can break the tiny safety circuit even when the flame looks strong.