Pilot Light Keeps Going Out: 6 Causes and Real Fixes
I'm Dan Reeves, a licensed master plumber with 20 years in residential work and more than 4,000 jobs behind me. A pilot light that keeps going out is one of the most common calls I run, and one of the most misdiagnosed at the kitchen table. People replace good thermocouples, ignore bad venting, and relight the same pilot a dozen times hoping it will behave. The pilot system is small — a flame, a sensor, a valve — and it fails in patterns. Read the pattern first and you will usually know the bad part before you touch a wrench. If your heater is not heating at all, my companion guide on [water heater not heating](/articles/water-heater-not-heating/) walks the full no-hot-water sequence; this one is for the pilot that lights, then betrays you.
I’m Dan Reeves, a licensed master plumber with 20 years in residential work and more than 4,000 jobs behind me. A pilot light that keeps going out is one of the most common calls I run, and one of the most misdiagnosed at the kitchen table. People replace good thermocouples, ignore bad venting, and relight the same pilot a dozen times hoping it will behave. The pilot system is small — a flame, a sensor, a valve — and it fails in patterns. Read the pattern first and you will usually know the bad part before you touch a wrench. If your heater is not heating at all, my companion guide on water heater not heating walks the full no-hot-water sequence; this one is for the pilot that lights, then betrays you.
One safety line before anything else, and I do not soften it: if you smell gas near the water heater, stop. Do not relight, do not flip switches, leave the house and call your gas utility or 911 from outside. Everything below assumes no gas smell.
Why does a pilot light keep going out?
The pilot has one job: prove to the gas valve that a flame exists, so it is safe to send gas to the main burner. The thermocouple is the proof. Its tip sits in the pilot flame, and heat on that tip generates a tiny voltage — millivolts — that holds a magnet open inside the gas control valve. Flame dies, voltage dies, magnet releases, gas stops. That chain is why a pilot problem is almost never random. Match your pattern to the table.
| What you observe | Most likely cause | First move |
|---|---|---|
| Lights fine, dies the instant you release the knob after 60 seconds | Failed or weak thermocouple | Replace thermocouple |
| Weak, lazy, mostly yellow flame | Dirty pilot orifice or low gas flow to pilot | Clean pilot tube and orifice |
| Stays lit hours or days, then out — often on windy days | Downdraft or venting problem | Inspect flue, vent cap, and draft hood |
| Pilot stays lit but main burner never fires | Gas control valve or thermostat fault | Pro diagnosis, likely valve |
| Soot, scorch marks, or a flame that lifts and roars | Combustion or venting fault — carbon monoxide risk | Shut it down, call a pro now |
| Went out once after a storm or utility work | One-off draft or gas interruption | Relight once and monitor |
The windy-day row deserves emphasis because it wastes more thermocouples than any other. If your pilot holds for days and dies when the wind picks up, the sensor is probably fine — a downdraft is blowing the flame off the thermocouple or out entirely. Check that the vent cap is intact and the flue is not blocked or separated before you buy parts.
How do you relight a pilot light, step by step?
Follow the lighting instructions printed on your tank if they differ from these — manufacturers vary. The standard sequence:
- Turn the gas control knob to OFF and wait at least 5 minutes. This lets any accumulated gas clear. If you smell gas during the wait, stop and leave.
- Turn the knob to PILOT. Press and hold it down — this manually opens the pilot gas port.
- Click the piezo igniter button repeatedly, or hold a long lighter to the pilot tip, until the pilot lights. Look for a steady blue flame.
- Keep holding the knob down for a full 30 to 60 seconds after it lights. This is the step everyone rushes. The thermocouple needs that time to heat up and start generating.
- Release the knob slowly. The pilot should stay lit on its own.
- Turn the knob to ON and set your temperature — the main burner should fire with a soft whoosh.
- Check the flame: strong, blue, and wrapping the thermocouple tip. A small yellow tip is normal; a mostly yellow, wandering flame is not.
If the pilot dies at step 5 twice in a row, stop relighting and diagnose. You have learned something real: gas is reaching the pilot, the flame lights, but the hold circuit is not holding.
How do you check the thermocouple before replacing it?
Three free checks first. Position: the thermocouple tip should sit in the flame, with roughly the top third of the tip bathed in blue flame. Tips slip out of position when the burner assembly gets bumped. Soot: a blackened, crusty tip insulates the sensor — a gentle clean with fine sandpaper or an emery cloth sometimes revives a marginal one. Connection: the thermocouple’s copper lead threads into the bottom of the gas valve, and it should be snug — finger tight plus a quarter turn with a wrench. A loose connection drops the millivolt signal just like a dead sensor does.
If all three check out and the pilot still will not hold, the thermocouple has earned its replacement. It is a $10 to $25 part at any hardware store — buy the right length, usually 24 to 36 inches, with the same thread style. The swap is a classic homeowner-level repair if you are careful: gas knob off, unthread the old lead from the valve, unclip the tip from the pilot bracket, route the new one the same way avoiding sharp bends, and snug the connection. Pros use a multimeter to confirm millivolt output, which is how I verify before condemning a valve.
What about drafts, venting, and the gas control valve?
Venting faults are the diagnosis people skip, and they matter beyond the nuisance. A disconnected or crushed flue, a missing vent cap, or a chimney with a bird’s nest will kill a pilot — and the same fault can spill combustion gases into the room while the burner runs. If your pilot history tracks the weather, or the heater lives in a tight closet that got more airtight after a remodel, think venting and combustion air before parts.
The gas control valve is the last suspect, not the first, because it is the expensive one. The thermocouple signal holds a magnet inside it; after years that magnet weakens. The tell is a pilot that will not hold with a verified-good thermocouple and a perfect flame. Valves also fail the other way — pilot holds, burner never fires, or temperature control goes erratic. There is no field repair for the valve body. It gets replaced whole, and sealed combustion and proprietary valve designs on newer units make that a pro job in my book.
Age is the tiebreaker. On a heater past 10 to 12 years, I will quote you a valve and a new tank side by side, because putting a $500 valve on a tank near the end of its life is how people spend replacement money twice. My guide to how long water heaters last lays out the age math I use.
How much does it cost to fix a pilot light that won’t stay lit?
| Repair | DIY cost | Pro cost | Notes |
|---|---|---|---|
| Relight and inspection | $0 | $75–$200 | Free if you do it; pro checks flame, venting, valve |
| Pilot orifice and burner cleaning | $0 | Usually in the service call | Fixes the weak yellow flame pattern |
| Thermocouple replacement | $10–$25 part | $150–$300 | The most common fix; mostly labor |
| Thermopile replacement (millivolt units) | $20–$40 part | $150–$300 | Found on some newer gas controls |
| Gas control valve replacement | Not recommended DIY | $300–$700 | Weigh against replacement if tank is 10+ years |
| Flue or vent repair | Varies | $200–$600 | Downdraft and cap problems live here |
Notice what is not on that table: a line for “keep relighting it.” Every repeat outage with no diagnosis is a safety system reporting a fault. The cheap repairs really are cheap — most pilot calls I close are a cleaning and a thermocouple, out the door under $300.
When should you call a pro about a pilot light?
Call immediately — before any DIY — if you smell gas, if you see soot or scorching around the draft hood, if the flame lifts, roars, or burns mostly yellow after cleaning, or if anyone in the house has headache or nausea that clears outdoors. That last one is a carbon monoxide flag, and it outranks hot water.
Call a pro in normal course if the pilot dies twice after a correct relight, if a new thermocouple does not hold, if the burner will not fire with the pilot lit, or if the unit uses a sealed combustion chamber you are not equipped to open. And if the heater is old and the quote is a gas valve, get the replacement quote in the same visit. A pilot system is simple, but it guards a gas appliance — treat its warnings with respect and it will run for years on pocket-change parts.
Frequently asked questions
Why does the pilot light but go out when I release the knob?
That pattern points straight at the thermocouple. When you hold the knob down, you are manually holding the gas valve open. The thermocouple has to heat up in the pilot flame and generate a small electrical signal that holds the valve open on its own. If the flame dies the second you let go after a full 30 to 60 seconds, the thermocouple is weak, dirty, misaligned, or dead. It is the most common pilot failure I see, the part costs $10 to $25, and a pro swap runs $150 to $300 installed.
Is it safe to keep relighting a pilot light that keeps going out?
Relighting once or twice to restore hot water is fine — that is what the instructions on the tank are for. Relighting it every day is not a solution, it is a symptom you are ignoring. A pilot that will not stay lit is the safety system doing its job, and repeatedly forcing it can mask a venting or combustion problem. My rule: if it goes out a second time within a week, stop relighting and diagnose. And if you ever smell gas — rotten eggs around the unit — do not relight anything. Leave, and call the gas utility from outside.
How much does it cost to fix a pilot light that won't stay lit?
It depends entirely on which part quit. A pro visit to relight and inspect runs $75 to $200. A thermocouple is a $10 to $25 part; installed by a plumber it is $150 to $300, mostly labor. A thermopile on a millivolt system runs $150 to $300 installed. The expensive one is the gas control valve: $300 to $700 installed, which on a heater over 10 years old should start a replacement conversation instead. Cleaning a clogged pilot orifice is usually folded into the service call at little or no extra charge.
Can a dirty pilot tube make the pilot keep going out?
Yes, and it fools people because the pilot still lights. Dust, lint, and spider webs partially block the tiny pilot orifice, so the flame comes out small, lazy, and yellow instead of strong and blue. A weak flame does not bathe the thermocouple tip properly, so the signal fades and the valve closes — sometimes right away, sometimes after a few hours. I clean the orifice and burner assembly before condemning any part. If your flame is mostly yellow and flutters, suspect dirt first and a failing thermocouple second.
How do I know if it is the gas valve and not the thermocouple?
Sequence tells the story. If a new or known-good thermocouple still cannot hold the pilot, and the flame is strong, blue, and wrapped around the sensor tip, the problem moves up the chain to the gas control valve — its internal magnet is what the thermocouple signal holds open, and magnets wear out. Other valve signs: the temperature dial stops regulating, the burner will not fire even with the pilot lit, or the knob feels gritty and stiff. Valve replacement is $300 to $700, and on an older tank I quote the valve and a new heater side by side.