On a gas water heater, a pilot that won’t stay lit often means a dirty pilot, weak thermocouple/thermopile, poor air or draft, or low gas supply.
Fast Checks Before You Grab Tools
Start simple. Set the gas control to “pilot,” hold the button, and watch the flame. You want a steady blue flame that reaches the tip of the sensor. If the flame is tiny, yellow, or waving around, the pilot can’t heat the sensor long enough to keep the gas valve open. Clear the area around the heater, remove lint at the base, and be sure the access panels are seated and secure after lighting.
Common Causes, Clues, And First Steps
| Probable Cause | What You Notice | What To Try |
|---|---|---|
| Dirty pilot orifice | Small or lazy flame | Shut gas off, let cool, remove dust; clean the pilot opening with compressed air |
| Thermocouple out of position | Flame hits side, not the tip | Gently center the flame on the last 3–5 mm of the sensor tip |
| Weak thermocouple/thermopile | Pilot lights, then drops out after button release | Retighten the nut finger-tight plus a quarter turn; replace if aged |
| Clogged air intake or flame arrestor | Sooting, faint flame, burner snuffs | Vacuum the base screen and arrestor; clear lint and pet hair |
| Backdrafting or wind | Pilot flickers when burner starts or with doors opening | Check vent connection and room make-up air; close windows that push wind |
| Low gas supply or closed valve | Weak flame on all tries | Verify gas cock is fully open; other gas appliances working? |
| Faulty gas control valve | All else checks out | Replace the control as per model instructions |
| Tripped thermal switch | No pilot after flammable vapor event or blocked air | After clearing intake, reset the switch if your model has one |
Gas Water Heater Pilot Won’t Stay Lit: Root Causes
Combustion Air Starvation
Most modern tanks use a flame arrestor and a screened air path under the burner. Dust, lint, or pet hair can choke that path. The pilot and main flame both suffer, and the safety system shuts the gas. Slide a vacuum nozzle around the base, brush the arrestor gently, and clear any side screens. Keep storage boxes a few feet away so the heater can breathe.
Draft And Venting Trouble
A downdraft from a shared chimney or a loose vent hood can upset the pilot. With the burner running, hold a smoking match near the draft hood; smoke should pull into the hood, not spill out. If it spills, tighten vent joints and space the vent from elbows per the manual. Wind from an open garage door can also puff out the flame; shield the area and restore the door to a normal position after lighting.
Thermocouple Or Thermopile Weakness
The sensor generates a small voltage from heat. If it’s loose, dirty, bent away from the flame, or worn out, the gas valve drops out as soon as you release the button. Seat the sensor tip in the heart of the flame, snug the connection at the valve (do not overtighten), and replace the part if the problem keeps coming back. Many newer heaters use a thermopile that feeds both the pilot circuit and electronics; failure feels the same.
Pilot Tube Or Orifice Debris
Spider webs and fine dust are common in pilot openings. Never stick a needle into the jet; that can change the orifice size. Use a burst of canned air aimed across the opening, or pull the assembly and clean from the back side with air only. Re-seat the tube and check for kinks before relighting.
Gas Supply And Valve Issues
Make sure the manual gas cock is open and the flex connector isn’t pinched. If other gas appliances seem weak or out, stop and call your gas supplier. If supply is fine and a fresh sensor and clear pilot still drop out, the gas control valve may be at fault. Match the replacement to your exact model and follow the lighting procedure after installation.
Safety First, Always
If you smell gas, leave the building, keep everyone out, and call the gas company or emergency services from a safe place. Do not relight or switch anything until responders say it is safe. The U.S. Consumer Product Safety Commission outlines these steps in its gas safety flyer, which mirrors utility guidance.
Step-By-Step: Relight And Test The Pilot
1) Prepare The Area
Turn the gas control to “off” and wait five minutes. Move cardboard boxes, paint, and rags away from the base. Remove the burner door or sight glass as your model requires.
2) Clean The Air Path
Vacuum the base ring and underside, then brush the flame arrestor. If your model has a resettable thermal switch near the viewing window, press it after cleaning.
3) Clean The Pilot Assembly
Shut the gas off at the manual valve. Once cool, disconnect the pilot tube and sensor from the control. Blow compressed air across the pilot orifice and through the tube. Reinstall the parts and route the tube without sharp bends.
4) Position And Snug The Sensor
Place the sensor tip so the blue cone of the pilot just kisses the last few millimeters. Tighten the nut finger-tight, then a quarter turn with a wrench. Re-check after the first firing.
5) Light And Observe
Follow the lighting label on the tank. Hold the pilot button down while lighting, then keep holding for 30–60 seconds. Release slowly. The pilot should stay on, the status light (if equipped) should blink, and the main burner should light when you set the control to “on.” Watch the flame for two to three minutes.
When Cleaning Isn’t Enough
Some failures point to parts replacement. The table below maps common symptoms to likely parts and the kind of task you’re taking on.
| Symptom | Likely Cause | DIY Level |
|---|---|---|
| Pilot holds only while button is pressed | Weak thermocouple or loose connection | Easy: replace sensor and snug fitting |
| Good pilot, burner never lights | Bad gas control or failed thermopile | Moderate: match parts and relight |
| Pilot weak or yellow | Dirty orifice or poor combustion air | Easy: clean pilot and intake |
| Pilot pops out during burner start | Backdraft or vent issue | Moderate: correct vent and hood |
| No pilot at all | Closed gas cock, tripped thermal switch | Easy: open valve; reset after clearing intake |
Brand Notes That Help
Bradford White Flame Arrestor Cleaning
Many Bradford White “Defender” models use a ScreenLok flame arrestor under the burner. If lint builds up there, the pilot can drop out as the burner starves for air. The service manual shows how to brush and vacuum that screen and how to reset the thermal switch after clearing a blockage. Use the exact steps for your series, then relight.
A.O. Smith Pilot Basics
A.O. Smith’s info center explains what the pilot does and how the lighting sequence works. If you understand the sequence, it’s easier to spot what’s missing: flame quality, sensor heat, or valve response. Use the label on your tank for the timing, since different controls vary.
Keep The Pilot Burning Reliably
Give The Heater Room To Breathe
Leave space around the base and avoid storing dust-making items next to the jacket. In a tight closet, add a louvered door or high-and-low grilles to supply make-up air as the manual allows.
Vacuum On A Schedule
Once or twice a year, turn the control to “pilot,” let the burner cool, and vacuum the intake screen and base. Wipe the burner door gasket and reseat it so the air path is correct after you’re done.
Check The Vent After Wind Events
Look for slipped joints, crushed vent pipe, or a missing draft hood clip. Re-seat the hood, keep the vent rising, and reduce long horizontal runs that can cause spillage at start-up.
Watch For Telltales
Rust streaks near the draft hood, scorch marks at the viewing port, or frequent resets of a thermal switch all point to poor air or venting. Fix those first, then reassess the pilot.
When To Call A Licensed Pro
Reach out if you have repeated drop-outs after cleaning and a new sensor, any sign of vent spillage, scorch marks, or you can’t get a steady blue flame. A pro can test draft, check manifold pressure, and verify valve operation with instruments.
Tool List For A Smooth Fix
Keep a small set on hand: shop vacuum with brush, soft bottle brush, canned air, adjustable wrench, screwdriver set, flashlight, and a replacement thermocouple or thermopile matched to your model. Keep spare matches and fresh batteries for your flashlight nearby and dry.
Quick Reference: What “Good” Looks Like
Pilot Flame
Sharp blue cone that touches the sensor tip and barely lifts off the pilot hood. No lifting, no yellow tips, and no whistling.
Sensor Placement
Tip centered in the hottest part of the flame, not buried in the blue cone. Lead routed clear of the burner so it doesn’t overheat.
Air Path
Clean intake screen, clear base, arrestor free of lint, and burner door sealed so air flows the way the manufacturer intended.
Final Checks Before You Close It Up
Set the control to “on,” confirm the main burner lights cleanly, then watch the draft hood with a smoke source to be sure the chimney pulls. Replace the access panels firmly and verify the status light pattern matches normal operation for your model. After one full heat cycle, sniff for gas and look for any water drips around the drain and relief valve.