Quick Answer: A water heater pilot light that won’t stay lit is most often caused by a failing thermocouple, the small sensor that confirms a flame is present before allowing gas to flow. A dirty pilot orifice, a draft in the area, or a failing gas control valve can also cause it. If you ever smell gas, stop immediately, don’t attempt to relight anything, ventilate the area, and contact your gas utility or a professional right away.
In This Article
- What the Thermocouple Actually Does
- Other Causes Worth Ruling Out
- Practical Steps to Relight and Diagnose It
- Warning Signs That Mean Stop and Call for Help
- Common Mistakes
- DIY vs. Professional Help
- Prevention
- Quick Pro Tips
- FAQs
- Key Takeaways
What the Thermocouple Actually Does
A thermocouple is a small safety sensor positioned in the pilot flame that confirms the flame is actually lit before allowing the main gas valve to open. When it wears out or gets slightly out of position, it stops sensing the flame properly, and the gas valve shuts things down as a safety response, even though the pilot may have lit successfully moments before. This is the single most common reason a water heater pilot light won’t stay lit, and it’s a relatively inexpensive part on its own, though the appliance’s gas connection means many homeowners reasonably prefer a professional to replace it.
Other Causes Worth Ruling Out
A dirty or partially blocked pilot orifice restricts gas flow enough that the flame burns too small or unevenly to keep the thermocouple properly heated. A draft in the area, from a nearby vent, door, or air handler, can physically blow out a marginal flame even if everything else is functioning normally. Less commonly, the gas control valve itself can fail internally, which is a more involved and costly repair than a thermocouple. Our guide on why your water heater makes popping or rumbling noises covers a separate but related maintenance item worth checking on any older gas unit.
Practical Steps
- Follow the exact relighting instructions printed on the panel of your specific water heater, since the process varies slightly by manufacturer.
- When holding the pilot button during relighting, hold it for the full duration specified in the instructions, often 30 to 90 seconds, to let the thermocouple heat sufficiently before releasing.
- If it lights but goes out as soon as you release the button, that pattern points specifically toward the thermocouple.
- If the flame looks weak, yellow, or uneven rather than a steady blue, check for a dirty pilot orifice or a draft in the area.
- If the pilot won’t light at all, even briefly, or if you smell gas at any point, stop and contact a professional rather than continuing to try.
Warning Signs
- Any smell of gas, at any point in this process, which means stopping immediately, not attempting to relight anything, ventilating the area, and contacting your gas utility or 911 from outside the home.
- A pilot flame that’s yellow or orange rather than a steady blue, which can indicate a combustion problem beyond a simple thermocouple issue.
- Soot or scorch marks around the pilot assembly, suggesting incomplete combustion that needs professional attention.
- A pilot that relights fine but the main burner doesn’t ignite properly afterward, which points toward the gas control valve rather than the thermocouple.
Common Mistakes
- Not holding the pilot button for the full time specified in the manufacturer’s instructions before releasing it.
- Repeatedly attempting to relight without addressing a possible draft or dirty orifice as the underlying cause.
- Continuing to try to relight the pilot after smelling gas, rather than stopping immediately and leaving the area.
- Assuming a failed thermocouple is a sign the whole water heater needs replacing, when it’s usually an inexpensive, isolated part.
DIY vs. Professional Help
Reasonable to DIY:
Following the printed relighting instructions and observing the flame’s color and behavior are reasonable for a homeowner to do.
Call a professional if:
Replacing a thermocouple or gas control valve involves working directly with gas components, and any gas smell at all means stopping immediately and contacting a professional or your gas utility rather than attempting a DIY fix.
Prevention
Having a gas water heater’s pilot assembly and thermocouple inspected during an annual maintenance visit catches a marginal thermocouple before it starts causing repeated outages. Keeping the area around the water heater free of drafts, and clear of stored items that could restrict airflow, also reduces one of the less obvious causes.
Quick Pro Tip: If your pilot lights but goes out the moment you release the button, note that pattern specifically when describing the problem to a plumber. It’s a strong, specific clue that points straight to the thermocouple rather than a broader gas valve issue.
FAQs
Q: Why does my water heater pilot light keep going out?
A: The most common cause is a failing thermocouple, the sensor that confirms the pilot flame is lit before allowing gas to flow. A dirty orifice, a draft, or a failing gas control valve can also cause it.
Q: Is it safe to keep trying to relight the pilot myself?
A: Following your water heater’s printed instructions to relight the pilot is generally fine. If you ever smell gas, though, stop immediately and don’t attempt to relight anything.
Q: How much does it cost to replace a water heater thermocouple?
A: The part itself is relatively inexpensive, though labor cost varies, and many homeowners reasonably choose a professional given the gas connection involved.
Q: What does it mean if the pilot flame is yellow instead of blue?
A: A yellow or orange flame can indicate a combustion problem beyond a simple thermocouple issue and is worth having a professional look at rather than continuing to relight it repeatedly.
Q: Can a draft really blow out a water heater’s pilot light?
A: Yes, particularly if the flame is already burning weak or small due to a dirty orifice, a nearby draft can be enough to extinguish it.
Key Takeaways
- A failing thermocouple is the most common reason a gas water heater’s pilot won’t stay lit.
- A dirty pilot orifice, a draft, or a failing gas control valve are the other common causes.
- Any gas smell means stopping immediately and calling a professional or your gas utility, not continuing to relight.
- Thermocouple replacement is an inexpensive part, though many homeowners reasonably prefer a professional given the gas connection.