How to Fix a Water Heater Pilot Light

Waking up to a cold shower because the water heater pilot light went out is a jarring experience, but it’s one of the more approachable home repair problems you’ll encounter. In most cases, relighting the pilot takes less than five minutes.

Waking up to a cold shower because the water heater pilot light went out is a jarring experience, but it’s one of the more approachable home repair problems you’ll encounter. In most cases, relighting the pilot takes less than five minutes. When the pilot keeps going out — or won’t stay lit after relighting — the fix is usually a worn thermocouple, a $10–$20 part that any homeowner can replace in half an hour.

This guide covers the complete diagnostic process: safely relighting the pilot, understanding why it keeps going out, replacing the thermocouple, and recognizing when the problem points to the gas valve or requires a professional.

Safety note: Natural gas and propane are serious hazards when mishandled. Before any work on a gas appliance, check for the smell of rotten eggs (the odorant added to gas). If you smell gas, do not light anything, do not flip light switches, leave the building immediately, and call your gas company. Only proceed with this guide if there is no detectable gas odor.

What You Need

Have these on hand before starting:

• Thermocouple Replacement — the most common fix when the pilot won’t stay lit
• Long-Reach Lighter — for water heaters without a built-in igniter button
• Adjustable Wrench — for disconnecting the thermocouple fitting
• Screwdriver Set — for removing the access panel
• Flashlight or Headlamp — the pilot assembly area is often dark
• Pipe Thread Compound or Thread Tape — if you need to reseat any gas fittings

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Understanding the Pilot Light System

Before diving into repairs, it helps to understand the components at play.

The pilot burner is a small, continuously burning flame that ignites the main burner when the thermostat calls for heat. On standing pilot models (the most common type in homes built before 2010), this flame burns continuously. On newer intermittent ignition models, an electronic spark ignites the pilot only when needed.

The thermocouple is a thin metal probe, about 12 inches long, positioned directly in the pilot flame. When the flame heats the tip, the thermocouple generates a small millivolt electrical signal. This signal travels down to the gas valve and tells it: “The pilot is lit. It’s safe to stay open.” The moment the flame goes out, the signal drops, the gas valve closes, and gas flow stops — a critical safety mechanism.

The gas valve is the main control unit mounted on the front of the water heater. It controls gas flow to both the pilot and the main burner, and it houses the temperature dial. A knob on the valve toggles between Off, Pilot, and your temperature settings.

The access panel is the small metal cover at the bottom front of the water heater that you remove to access the pilot assembly.

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Step 1: Relight the Pilot Light

Start here before buying any parts. Pilots go out for simple reasons — a draft, a temporary gas supply interruption, or a momentary flame disruption — and can be relit in minutes.

1. Find the instruction label. Almost every water heater has a relighting instruction label affixed to the front of the unit. Read it before proceeding — the exact steps vary slightly by manufacturer and model.

2. Turn the gas valve to “Off.” Locate the gas control valve knob and turn it to the “Off” position. Wait a full 5 minutes. This allows any accumulated gas in the area to dissipate before you introduce a flame.

3. Remove the access panel. Unscrew or unclip the small panel at the bottom front of the water heater to expose the burner assembly and pilot tube.

4. Set the gas valve to “Pilot.” Turn the knob from “Off” to the “Pilot” setting.

5. Press and hold the pilot button. On most valves, pressing the knob down (or pressing a separate red pilot button) manually opens the gas supply to the pilot tube. Keep it pressed firmly.

6. Ignite the pilot. If your water heater has a built-in igniter button (a small separate button, often red or black), press it once per second while holding the pilot knob down. You’ll hear a click and see the pilot flame ignite. If there’s no igniter, use a long-reach lighter to light the pilot at the burner while pressing the knob.

7. Hold for 30–60 seconds. After the pilot lights, continue holding the pilot knob down for at least 30–60 seconds. This heats the thermocouple enough to generate a sustaining current. Releasing too early is the most common relighting mistake.

8. Release the button slowly. After holding for 60 seconds, slowly release the pilot knob. The pilot should remain lit. If it goes out immediately, wait five minutes and try again, this time holding for a full 90 seconds.

9. Set the thermostat. Once the pilot is confirmed lit, turn the gas valve knob to your desired temperature setting (usually the “Hot” or 120°F marker). Replace the access panel.

If the pilot stays lit and your water heater returns to normal operation, you’re done. If the pilot goes out again within a few hours or days — or won’t stay lit at all — continue to Step 2.

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Step 2: Clean the Thermocouple

Before replacing the thermocouple, try cleaning it. A coating of dust, soot, or mineral buildup on the thermocouple tip can insulate it enough to prevent proper signal generation.

Turn the gas valve to “Off” and let the unit cool for 15–20 minutes. Locate the thermocouple — it’s the thin copper tube that runs from the pilot assembly down to the gas valve. Use fine steel wool or light sandpaper to gently clean the tip of the thermocouple (the end that sits in the flame). Be careful not to bend or kink the copper tube.

Relight the pilot following Step 1. If it now stays lit consistently, a dirty thermocouple was the culprit. Monitor over the next few days. If it goes out again, the thermocouple itself needs to be replaced.

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Step 3: Replace the Thermocouple

Thermocouple replacement is the solution for about 80% of “pilot won’t stay lit” problems. The part costs $10–$20 and the replacement takes 20–30 minutes.

Purchase the right thermocouple. Check your water heater’s model number (on the label on the side of the unit) and look for a thermocouple that matches. A universal water heater thermocouple will fit most standard units. Pay attention to length — thermocouples come in 18”, 24”, and 36” lengths. The new one should match the length of the old one.

Turn off the gas and let it cool. Turn the gas valve to “Off.” Give the unit 20–30 minutes to cool, especially the thermocouple and pilot assembly, which get hot during operation.

Locate the three connections. The thermocouple connects to the system in two places:

• The tip end sits in the pilot flame, held in a bracket at the pilot assembly.
• The other end (a threaded fitting) screws into the bottom of the gas valve.

Disconnect the thermocouple from the gas valve. Use an adjustable wrench to unscrew the thermocouple nut from the gas valve. Turn counterclockwise. It should unthread with modest force — don’t force it if it’s very tight, as the gas valve fitting is soft metal.

Remove the thermocouple tip from the pilot bracket. At the pilot assembly, the thermocouple tip is held in a small clip or bracket. Slide it out or press the clip to release it. Note exactly how it was positioned relative to the pilot flame — the new one needs to sit in the same position.

Install the new thermocouple. Feed the new thermocouple into position, clip the tip into the pilot bracket in the same position as the old one (the tip should sit in the path of the pilot flame), and hand-tighten the nut onto the gas valve fitting. Use the wrench to snug it — about 1/4 turn past hand-tight. Don’t overtighten.

Relight the pilot. Follow the Step 1 relighting procedure. Hold the pilot button for 60 seconds. A new thermocouple will heat up and generate signal properly almost immediately. The pilot should stay lit reliably after release.

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Step 4: Check the Thermocouple Position

Even a brand-new thermocouple will fail to keep the pilot lit if it’s not positioned correctly in the flame. The thermocouple tip needs to be engulfed in the pilot flame — not just touching it from the side, but sitting fully within it.

With the access panel off and the pilot lit, observe the flame. The pilot flame should be:

• Blue with a small orange tip
• Steady, not flickering excessively
• Directly touching the thermocouple tip

If the flame is too small (barely visible), the pilot orifice may be partially clogged. Use a can of compressed air to blow into the pilot tube area while the gas is off. Don’t insert wire into the pilot orifice, as this can damage it.

If the flame is wrapping around the thermocouple but still going out, try gently bending the thermocouple holder so the tip is more centered in the flame.

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Step 5: Test the Thermocouple with a Multimeter (Optional)

If you want to confirm a failing thermocouple before replacing it, a quick multimeter test gives you a definitive answer.

Set a multimeter to the DC millivolt (mV) setting. Light the pilot and hold it for 60 seconds. Disconnect the thermocouple from the gas valve, touch the multimeter probes to the thermocouple fitting and the tube body, and read the output.

A healthy thermocouple produces 25–35 mV while the tip is in the flame. A reading below 20 mV indicates a weakening thermocouple that needs replacement. A reading at or near 0 mV with the tip in a flame means the thermocouple has failed entirely.

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When the Gas Valve Is the Problem

If you’ve replaced the thermocouple and the pilot still won’t stay lit — or stays lit briefly (1–2 minutes) and then goes out — the gas valve itself is the likely culprit. A failed gas valve can’t maintain proper operation even with a working thermocouple.

Signs of a failed gas valve:

• Pilot lights and stays on for 1–5 minutes then extinguishes
• Clicking the igniter produces no spark or no gas flow
• The temperature setting doesn’t change the water temperature
• The unit is over 10 years old and has had multiple repairs

Gas valve replacement costs $100–$200 for the part. The install involves disconnecting gas lines, which is technically DIY territory in most areas, but many homeowners and local codes prefer professional installation for gas component work. Given the total repair cost ($150–$300 with labor) versus the cost of a new water heater ($500–$900 installed), replacement often makes more financial sense for units over 10 years old.

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Intermittent Electronic Ignition Systems

Homes built after approximately 2010 often have water heaters with intermittent or direct spark ignition rather than a standing pilot. These units don’t have a continuously burning pilot flame — instead, an electronic control module creates a spark each time the thermostat calls for heat.

On these systems, “pilot light problems” typically manifest as the burner not lighting at all. Diagnosis is more complex and involves checking the ignitor, flame sensor, and control board. These systems are better handled with professional service if basic troubleshooting (checking power supply, resetting the unit per manufacturer instructions) doesn’t resolve the issue.

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Preventive Maintenance for Water Heater Longevity

Pilot light problems are often a symptom of a water heater that hasn’t received regular maintenance. These practices extend water heater life significantly:

Flush the tank annually. Sediment buildup at the bottom of the tank reduces efficiency and causes the rumbling sounds some tanks make. Connect a garden hose to the drain valve, turn off the cold water supply, and drain a few gallons until the water runs clear.

Test the pressure relief valve. This safety valve should be tested once per year. Lift the lever briefly to confirm it opens and releases. If it doesn’t open or leaks after testing, it needs replacement.

Check the anode rod every 3–5 years. The sacrificial anode rod prevents tank corrosion. When it’s depleted, the tank itself begins to corrode. Inspecting and replacing it on schedule can double the useful life of a water heater.

Keep the area around the water heater clear. Drafts from nearby doors, windows, or HVAC vents can extinguish the pilot. Ensure the area has adequate clearance per manufacturer instructions (usually 18 inches minimum around the unit).

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Cost Summary

Repair	DIY Parts Cost	Pro Service Cost
Relight pilot	$0	$75–$100
Clean thermocouple	$0	$75–$100
Replace thermocouple	$10–$20	$150–$200
Replace gas valve	$100–$200	$250–$400
New water heater (installed)	—	$500–$900

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Related Reading

• How to Fix a Toilet That Keeps Running
• How to Fix a Washing Machine That Won’t Drain
• How to Unclog a Kitchen Sink Drain
• How to Fix a Leaky Faucet

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A water heater pilot light that won’t stay lit is almost always a thermocouple problem, and replacing it is a repair any homeowner can handle. Start by relighting the pilot and holding the button long enough — most failed relighting attempts are simply a matter of not waiting long enough for the thermocouple to heat up. If that doesn’t solve it, swap the thermocouple. For $10–$20 in parts and 30 minutes of your time, you’ll have hot water back and a skill that will serve you for decades.