A gas water heater that keeps shutting off points to a dirty pilot, weak flame sensor/thermocouple, draft, or low gas supply.
Ice cold showers, a blinking status light, and a burner that won’t stay on—when a tank heater keeps going out, the fix usually sits in a short list of causes. This guide gives clear steps to pinpoint the fault, safe relight instructions, and the checks that keep the flame steady.
Fast Diagnosis: Symptoms And What They Point To
Start with what you can see, smell, and hear. Flame color, gas odor, vent draft, and the status light code tell a story. Use the table below to match the symptom with a likely cause and a quick next move.
| Symptom | Likely Cause | Quick Check |
|---|---|---|
| Pilot lights, then dies on release | Weak thermocouple/thermopile or loose connection | Hold knob longer; confirm tip sits in the flame; snug the connection |
| No pilot spark | Igniter, wire, or piezo issue | Watch for spark through sight glass; inspect the lead and boot |
| Small yellow, lazy pilot | Dirty pilot or low gas pressure | Clean pilot orifice; make sure the gas valve is open |
| Pilot goes out on windy days | Backdraft or room draft | Check vent draw with match smoke; look for gaps around doors |
| Status light shows “flammable vapor” | FVIR sensor lockout | Remove fumes, air out space, then reset per valve instructions |
| Burner booms or pops | Sediment or delayed ignition | Flush tank; inspect burner and air shutter |
| Soot around burner door | Poor combustion or blocked vent | Inspect vent path, intake screen, and room air openings |
Safety First Before Any Relight
Do a sniff test. If there’s gas odor, shut the supply off, open doors, and step outside to call the utility or a licensed technician. Skip switches, lighters, and power tools until the area is clear.
Add a working CO alarm near sleeping areas and near the appliance zone. Poor combustion or a blocked vent can release carbon monoxide; an alarm is a lifesaver and should be part of your routine test schedule. For step-by-step pilot lighting, use your model’s panel label and a trusted guide like A. O. Smith’s pilot relight instructions.
Step-By-Step: Relight And Basic Checks
1) Confirm Gas Supply
Trace the gas line to the shutoff. The handle should align with the pipe. If the unit was newly installed or service was interrupted, air in the line can delay ignition; several cycles may be needed before the pilot holds.
2) Follow The Lighting Label
Every tank includes directions on the front panel. Set the control to “Pilot,” press and hold the knob, then use the spark igniter or a long lighter as directed. Keep the knob depressed for 60–90 seconds so the safety device warms and makes voltage.
3) Wait Ten Minutes If It Doesn’t Light
Turn the control to “Off” and let the chamber air out for at least ten minutes. That clears unburned gas and lets built-in safeties reset. Then repeat the relight steps.
4) Read The Flame
A healthy pilot is steady and mostly blue, aimed at the sensor tip. A weak, wavering, or yellow flame points to dust in the orifice, low pressure, or drafts. Fix those first, then test again.
Pilot Keeps Going Out: Common Causes And Fixes
Thermocouple Or Thermopile
This small probe makes a tiny voltage when heated by the pilot; that signal keeps the safety valve open. If the tip isn’t in the flame, is sooty, or has failed, the pilot dies the moment you release the knob. Re-seat the tip, clean with fine steel wool, and snug the connector. If you can meter it, compare readings to the maker’s spec; replace the part if it’s low or unstable.
Flame Sensor On Electronic Ignition
Many newer tanks sense flame with a metal rod instead of a standing pilot. A thin oxide layer can block the signal. Gently clean the rod, verify the ground path, and check the harness. If the board still won’t sense flame, a technician should test the circuit.
Dirty Pilot Orifice
Lint and dust collect in the tiny pilot jet. Shut gas off, remove the tube carefully, and blow the orifice clean with compressed air. Don’t ream or enlarge it.
Drafts, Backdraft, And Makeup Air
Wind, a garage door, or a tight closet can push or pull air in ways that snuff the flame. Check that the vent has proper rise and no gaps, the draft hood is centered, and the room has enough free area for combustion air. A louvered door or added grille often stops repeat outages in small closets.
Flammable Vapor Sensor Trip
FVIR systems lock out when they detect fumes. Remove solvents, gasoline, or paints from the area, ventilate, and reset the valve per your model’s procedure. If the sensor measures out of range after cleanup, replace it before further use.
Gas Pressure Problems
Low inlet pressure shrinks the pilot flame. Confirm the appliance shutoff is open and other gas loads aren’t starving the line. Pressure and regulator checks belong to the utility or a licensed pro.
Sediment And Overheating
Heavy mineral layers trap heat, make the burner roar, and can trip limit switches. A full tank flush and restored combustion air often stop nuisance shutdowns.
Close Variant: Gas Water Heater Keeps Going Out — What To Check Next
Once the flame holds, confirm steady combustion and safe venting so the fix lasts. Work through these checks in order.
Confirm Vent Draft
With the burner running, hold a smoking match near the draft hood. Smoke should pull into the hood. If it spills out, stop and bring in a vent pro to correct slope, length, or blockage.
Inspect The Air Intake Screen
FVIR tanks draw through a screen under the burner. A clogged screen starves the flame and triggers lockout. Vacuum the screen and the floor beneath the unit. Keep storage boxes a few feet away.
Check Connections And Ground
Loose spade connectors or a poor ground interrupt flame sensing. Reseat each connector and clean contact points. Look for brittle wire insulation near the burner door.
Read The Status Light Code
Modern gas valves blink a code. The chart on the heater door translates flash counts to a fault group—ignition, flame sense, overheat, or vapor lockout. Use that code to target the part or condition. Many brands also host code guides in their online owner centers.
Standing Pilot Vs Electronic Ignition
Standing pilot: A small flame burns nonstop and heats a thermocouple or thermopile. Common failures include a dirty pilot, a weak thermocouple, or drafts. The upside is simple parts and quick visual checks.
Electronic ignition: A spark or hot surface igniter lights gas on demand and the control board watches a flame rod. Common failures include a dirty flame rod, poor ground, a weak igniter, or control faults. Diagnosis leans on status codes and measurements.
How Pros Test A Thermocouple Or Thermopile
When a meter is handy, a quick test removes doubt. After the pilot burns a few minutes, measure open-circuit millivolts at the thermocouple leads and compare to the maker’s spec. If the signal collapses under load or can’t meet spec, replacement is the cleanest path.
| Component | Typical Reading | Action |
|---|---|---|
| Thermocouple (standing pilot) | ~25–35 mV open; lower under load | Below spec or unstable — replace |
| Thermopile (electronic valve) | ~300–800 mV | Low output — clean flame path; replace if still low |
| Flame rod (sense current) | Microamp range | Clean rod; verify ground and board input |
Cold Weather, Wind, And Venting Quirks
Strong wind can flip the draft at the hood, push flames off the pilot, or pull the flame away from the sensor. A loose vent joint, crushed connector, or long flat run raises the odds of spillage. Correct slope, tight joints, and a short straight rise help restore stable draft.
Room Air And Closets
Small closets often lack the free area needed for combustion air. If the flame starves, status codes and flame dropouts follow. Many installs benefit from high and low wall grilles or a louvered door. In tight homes, a sealed-combustion model that brings air from outside solves repeat outages.
Maintenance That Prevents Repeat Outages
- Vacuum the intake screen and burner area.
- Flush sediment yearly to keep heat transfer steady.
- Keep storage a few feet from the base and intake.
- Set the thermostat near 120°F for comfort and safety; the DOE temperature guidance explains why higher settings waste energy and raise scald risk.
- Test the CO alarm monthly; replace per the maker’s date code.
When Cleaning Isn’t Enough
Gas Control Valve Failure
Internal safety circuits age. If the pilot stays strong yet the valve drops out or throws repeat codes, plan on replacement. That job includes leak checks and should be handled by a licensed tech.
Venting Errors Or Blockage
Long horizontal runs, crushed connectors, bird nests, or a collapsed liner cause spillage and flame outages. A vent test under load and a quick cleanout often bring a steady draft back.
Room Air Starvation
Closet installs with tight doors and no grilles starve the flame. Add grilles or ducted openings sized to code, or switch to a sealed-combustion model.
Cost, Time, And DIY Boundaries
Simple cleaning, a new thermocouple/thermopile, or a flame-rod polish are within reach for many homeowners. Gas valve swaps, regulator issues, and vent redesigns belong to pros. If there’s gas odor, soot, or backdraft at the hood, schedule service right away.
Printable Checklist: Stabilize The Flame
Tools
- Shop vacuum and soft brush
- Nut drivers and a small adjustable wrench
- Multimeter with mV range
- Compressed air can
- CO alarm test button
Sequence
- Set gas to “Off,” wait ten minutes.
- Clean intake screen and burner area.
- Relight per the panel label or your brand’s guide (see the A. O. Smith link above).
- Verify a blue, steady pilot aimed at the sensor tip.
- Check draft with smoke; fix vent slope, joints, or blockages.
- Meter the thermocouple/thermopile if dropouts continue; compare to specs.
- Replace failed parts; call a licensed tech for valve, regulator, or vent work.
Stay Safe Around Combustion
A pilot that quits can be a simple maintenance task—or a clue that air or venting isn’t right. Keep solvent cans, paints, and gasoline away from the heater area, fit a CO alarm, and lean on pros whenever there’s doubt. For background on CO safeguards around gas appliances, see the U.S. Consumer Product Safety Commission guidance.