Short answer: When a water heater pilot light won't stay lit, the most common cause is a worn or dirty thermocouple (or thermopile) that no longer senses the flame. Other causes include a clogged pilot tube, a dirty flame arrestor screen, a draft, a kinked gas supply or a failing gas control valve. Most fixes are quick for a pro.
You relight the pilot, it burns for a few seconds, and then it goes out the moment you let go of the button. Or it stays lit for a day and goes out again. This guide covers the six most common causes, what is safe to check yourself and when to call our gas water heater repair team in Newark.
Safety first: If you smell gas, do not try to relight anything. Leave the house and call your gas utility or 911 from outside.
How does the pilot system work?
A standing-pilot gas water heater has three key parts:
- The pilot: a small flame that is always on.
- The thermocouple (or thermopile on some models): a metal sensor that sits in the pilot flame and makes a tiny electrical signal when it is hot.
- The gas control valve: it keeps gas flowing to the pilot only while it "hears" the signal from the thermocouple.
If the signal is weak or missing, the valve shuts off the gas, and the pilot goes out. It's a safety feature. Most pilot problems come down to something breaking that chain.
6 reasons a water heater pilot light won't stay lit
1. A worn or dirty thermocouple
This is the number one cause. Over time, the thermocouple tip gets coated or wears out. It can no longer make a strong enough signal.
Classic sign: The pilot lights while you hold the button, then goes out when you let go.
Fix: Replace the thermocouple. It is an inexpensive part, but on newer sealed-burner heaters it can be part of a larger assembly.
2. The thermocouple is out of position
If the thermocouple tip is not sitting right in the pilot flame, it won't get hot enough.
Fix: A pro can adjust it so the flame wraps the tip.
3. A clogged pilot tube
Dust, spider webs or soot can partly block the small pilot tube. The flame becomes weak, yellow or split, and it doesn't heat the thermocouple well.
Fix: Clean the pilot assembly. A healthy pilot flame is mostly blue and steady.
Tried relighting and it still won't hold?
Call us. We carry common thermocouples and pilot parts.
4. A clogged flame arrestor screen
Most gas water heaters made in recent years have a sealed combustion chamber with a screen at the bottom called a flame arrestor. It lets air in but blocks flames from getting out. In basements and laundry rooms, lint and dust can clog it, and the burner and pilot can starve for air.
Classic sign: The pilot goes out when the main burner fires, or after the heater runs for a while.
Fix: The screen must be cleaned, often by removing the burner assembly. This is a pro job on most models.
5. Drafts or venting problems
A strong draft near the heater can blow the pilot out. So can a vent that isn't drafting properly. Poor venting is also a carbon monoxide risk.
Fix: A pro should check the vent, draft and combustion air. Don't ignore this one.
6. A failing gas control valve
If the thermocouple is good and the pilot is clean, the gas control valve itself may be failing. Its internal magnet can no longer hold the pilot gas open.
Fix: Replace the gas control valve. On an older tank, replacing the whole heater may make more sense.
What you can safely check yourself
- Read the lighting label on the heater and follow it exactly.
- Hold the pilot button for the full time listed on the label (often 30 to 60 seconds) after lighting.
- Look at the flame through the sight glass. It should be blue and touch the thermocouple tip.
- Check for drafts from an open window, fan or door near the heater.
- Make sure the gas valve on the supply pipe is fully open.
- Keep the area clean. Don't store boxes, laundry or chemicals near the heater.
Quick guide: symptom vs. cause
| What happens | Most likely cause |
|---|---|
| Lights, goes out when you release the button | Thermocouple |
| Weak, yellow or split pilot flame | Dirty pilot tube |
| Goes out when the burner fires | Flame arrestor or venting |
| Goes out randomly | Draft or failing thermocouple |
| Won't light at all | Gas supply, igniter or valve |
| Stays lit, but no main burner | Gas valve or thermostat setting |
How to prevent pilot light problems
- Keep lint and dust away from the base of the heater, especially near a dryer.
- Vacuum the flame arrestor screen gently with the gas off, if your model allows.
- Don't store paint, gas cans or cleaners near the heater.
- Keep the vent clear and look for soot or rust at the draft hood.
- Book yearly maintenance so a tech can check the thermocouple and burner.
Local note: Many homes around Newark and in Pike Creek have gas water heaters next to a washer and dryer, and lint is a top reason flame arrestors clog. Propane units in parts of Hockessin use different pilot parts, and old chimney venting in Wilmington rowhomes can cause drafts that blow a pilot out. A yearly check during water heater maintenance can prevent it.
Related reading: Work through other causes with our no hot water troubleshooting guide, learn how to flush a water heater to keep the burner area cleaner, and check whether repeated outages are among the signs your water heater is going out.
When should you call a water heater professional?
Call a pro if:
- The pilot goes out more than once
- The flame is weak, yellow or lifting off the thermocouple
- It goes out when the main burner fires
- You ever smell gas
- You see soot or scorch marks at the burner door
Pilot, thermocouple and gas valve work involves gas lines and combustion. In Delaware, it falls under a state plumbing or HVAC license.
Pilot light won't stay lit in Newark? Call (302) 732-0874 for gas water heater repair from Newark Heater Pros, 24/7.
Frequently asked questions
How much does it cost to replace a thermocouple?
A thermocouple is a small, inexpensive part, so the repair is usually one of the lower cost gas water heater fixes. The final cost depends on the model, since sealed burner assemblies take more time.
Is it dangerous if the pilot light keeps going out?
The gas valve is designed to shut off gas when the pilot goes out, so it is usually not dangerous by itself. But if you smell gas, or the pilot goes out because of poor venting or a lack of air, it can be a safety issue.
Why does my pilot light go out when the burner turns on?
This often points to a venting or combustion air problem. When the main burner fires, a poor draft or starved air supply can snuff out the pilot. A pro should check the vent and the flame arrestor.
How much does it cost to replace a thermocouple?
The part itself is inexpensive. The total depends on access, whether the burner needs cleaning and whether the gas valve is the real problem. Ask for a written price before work starts.
Can I use hot water if the pilot keeps going out?
Only what is already in the tank. Do not keep relighting a pilot that will not hold. Repeated relights can mean a gas or venting problem.
