Why Your Water Heater Pilot Light Keeps Going Out (4 Causes)

TL;DR: A water heater pilot light that won't stay lit is caused by one of four things: a worn thermocouple (the most common, $20-40 in parts), a draft or venting problem, dirt clogging the pilot orifice, or a failing gas control valve ($200-400 to replace). Most homeowners can diagnose which one in under 10 minutes by checking the thermocouple's millivolt reading and looking for drafts near the burner compartment.

_Last reviewed: July 2026 · 6 min read_

Relighting the same pilot light three times in a week gets old fast, especially when the tank is 10 years old and you're not sure if this is a $20 fix or the start of a full replacement. The good news is that a pilot going out repeatedly almost always points to one of four specific problems, and you can narrow it down yourself before calling anyone.

Okoniq Property Hub logs appliance ages, repair dates, and part numbers so you're not guessing whether last year's thermocouple swap was on this unit or the last one.

Is a worn thermocouple the most likely cause?

Yes — the thermocouple is responsible for roughly 7 out of 10 pilot-light complaints on gas water heaters. It's a thin copper rod that sits in the pilot flame and generates a small electrical current, around 25 to 30 millivolts, that tells the gas control valve it's safe to keep gas flowing. Once that reading drops below about 20 millivolts, usually from years of heat cycling or a buildup of soot on the tip, the valve reads it as "flame out" and shuts the gas off even while the pilot is still burning.

You can test this with a multimeter set to millivolts DC, clipped to the thermocouple lead while the pilot is lit and held down for 30 seconds. A reading under 20 mV confirms the part is failing. Replacement thermocouples run $10 to $20 at a hardware store, and swapping one takes about 20 minutes with a wrench, though a plumber will typically charge $150 to $300 for the same job if you'd rather not do it yourself.

Could a draft be blowing the pilot out?

Yes, and this is easy to miss because the flame looks fine right up until it doesn't. If the pilot goes out only on windy days, only when the furnace or dryer kicks on, or only after someone closes a nearby door hard, you're likely dealing with a draft problem rather than a parts failure. Water heaters installed in basements, garages, or utility closets near exterior vents are the most common victims, and the same air-pressure imbalances that mess with drafts can also affect attic ventilation and combustion appliances throughout a house.

Check the burner compartment door and cover panel for gaps, and confirm the vent pipe above the tank has proper clearance and a good seal at each joint. If you closed up a vacation home or seasonal property for the winter, as covered in closing a seasonal home for the off-season, a disturbed flue connection is a common cause of pilot problems when the property is reopened.

Is a dirty pilot orifice choking the flame?

Sometimes, and it's the cheapest fix on this list if it's the culprit. Dust, spider webs, and mineral deposits can partially clog the tiny opening the pilot gas flows through, causing a weak, small, or lazy-looking flame that doesn't fully engage the thermocouple tip. A healthy pilot flame should be blue with a small yellow tip, roughly half an inch to an inch tall, and it should wrap around the thermocouple, not lean away from it.

| Symptom | Likely Cause | |---|---| | Flame is small, yellow, or lazy | Dirty orifice or low gas pressure | | Flame is strong but goes out after a few minutes | Worn thermocouple | | Flame goes out only on windy days or when doors slam | Draft problem | | Pilot won't even light, or clicking with no ignition | Gas control valve or ignitor issue |

Cleaning the orifice usually means shutting off the gas, removing the pilot assembly, and running a fine wire (never a toothpick, which can break off inside) through the opening. If you're not comfortable with gas lines, this is a reasonable moment to call a plumber rather than improvise.

When does the gas control valve need replacing?

When you've replaced the thermocouple, confirmed there's no draft, cleaned the orifice, and the pilot still won't hold, the valve itself is the remaining suspect. Gas control valves combine the thermocouple sensor, gas regulator, and temperature dial into one unit, and internal solenoid failures are common once a tank passes 10 to 12 years old. Replacement valves cost $150 to $250 in parts, plus another $150 to $250 in labor if a licensed plumber does the swap, since it involves working directly on the gas supply line.

At that price point, it's worth asking a plumber to quote both the valve replacement and a full new water heater, since a tank old enough to need a control valve is also close to the end of its typical 8 to 12 year lifespan. This is the same math worth running before sinking money into boiler maintenance on an aging heating system — sometimes the repair cost tips the scale toward replacement.

Should you check the venting before you touch anything else?

Yes, if the water heater shares a flue with a furnace or shares a chimney with a fireplace. Backdrafting from a blocked or undersized flue can starve the pilot of oxygen and mimic a thermocouple failure, and it's worth ruling out before spending money on parts. This is closely related to the checks covered in a chimney and fireplace inspection — soot staining above the draft hood, a rusted or disconnected vent connector, or a shared flue that's undersized for both appliances are all red flags a professional inspection will catch.

FAQ

How much does it cost to fix a water heater pilot light?

A thermocouple replacement runs $10 to $20 in parts if you do it yourself, or $150 to $300 with a plumber. A full gas control valve replacement runs $300 to $500 including labor.

Can I light the pilot myself, or do I need a plumber?

Most gas water heaters have a simple push-button ignition and instructions printed on the front panel, and lighting it yourself is safe if you follow the steps and smell for gas first. If you smell gas, hear hissing, or the pilot won't stay lit after two attempts, stop and call a licensed plumber.

How long do water heater thermocouples last?

Most thermocouples last 6 to 10 years before the copper degrades enough to fail, though heavy use or a consistently dirty burner compartment can shorten that.

Is a water heater pilot light supposed to stay on all the time?

Yes, on a standing pilot system the small flame burns continuously so the tank can reignite the main burner instantly when hot water is needed. Some newer models use electronic ignition instead and have no standing pilot at all.

When should I just replace the water heater instead of repairing it?

If the tank is past 10 years old and needs a $300+ valve replacement, or if you're seeing rust-colored water or a rusted tank base alongside the pilot issue, replacement is usually the better value than another repair.

This is educational information, not professional advice. Call a licensed plumber or gas technician if you smell gas, see rust or corrosion near the gas line, or aren't confident working with gas appliances.