Water Heater Pilot Light Keeps Going Out? Causes and Fixes

You step into the shower expecting hot water and get a lukewarm surprise. Down in the basement or utility closet, the little blue flame under the water heater is out again — for the third time this month. A pilot light that will not stay lit is one of the most common complaints on a gas water heater, and it almost always comes down to one of a few parts or conditions.

Relighting the pilot is a safe homeowner task when you follow the manufacturer's label. Diagnosing why it keeps going out is a different matter, because it involves gas, combustion air, and venting. This guide explains how the pilot system works, what to check safely, which parts commonly fail, and the point at which a professional should take over.

How a Pilot Light and Thermocouple Work

Older and mid-efficiency gas water heaters use a standing pilot: a small flame that burns continuously next to the main burner. When the thermostat calls for heat, the gas control valve opens and the burner lights from that pilot flame.

A pilot cannot simply burn unattended. A safety device called a thermocouple sits in the flame and generates a tiny electrical current as it heats. That current holds the gas valve open. If the flame goes out, the thermocouple cools within seconds, the current stops, and the valve closes so gas cannot keep flowing into an unlit burner.

This is why a pilot that lights but will not stay lit after you release the button usually points to the thermocouple. It is also why the button must be held down for a period during relighting — you are waiting for the thermocouple to get hot enough to hold the valve open.

Safety First: Gas Odor, Venting, and Air Supply

Before touching anything, trust your nose. If you smell gas — the sharp, sulfur-like odor added to natural gas and propane — do not light a match, flip a switch, or use a phone near the heater. Leave the building, get everyone outside, and call your gas utility or emergency services from a safe distance. A pilot that will not stay lit is never worth risking a gas leak.

Other safety basics:

• Keep the area around the heater clear of paint cans, gasoline, solvents, and stored boxes.
• Make sure the heater has unobstructed combustion air. A closet with a sealed door or a pile of laundry blocking the louvers can starve the flame.
• Check that the vent pipe is connected, sloped correctly, and not corroded or blocked. A backdraft can blow out the pilot and send exhaust into the room.
• Confirm a carbon monoxide alarm is working on every level of the home and near sleeping areas.
• Never store flammable items against the tank, and never use a heater with a damaged flue.

If the heater sits in a tight closet, leave the door ajar as the manufacturer allows. A pilot flame that flutters or lifts off the burner is a sign of a draft or air problem, not a weak flame.

Relighting the Pilot: Follow the Label

Every gas water heater has a label near the gas control valve with lighting instructions specific to that model. Read it rather than relying on a video for a different brand. The general sequence is similar on most standing-pilot units, but the knob positions and wait times vary.

1. Set the temperature dial to the lowest setting and turn the gas control knob to the pilot position, as the label directs.
2. Wait the recommended period — often several minutes — so any residual gas can clear before you bring a flame near the burner.
3. Hold the control knob down and press the igniter button, or apply a long lighter to the pilot assembly if the label permits it. Keep your hands and sleeves clear of the burner.
4. Continue holding the knob for the full time stated on the label after the flame lights, usually around 30 to 60 seconds.
5. Release the knob. If the flame stays lit, turn the knob to the desired setting and replace the access panel.

If the pilot goes out the moment you release the knob, stop and repeat once. Repeated attempts with the same result indicate a failed thermocouple or another fault that needs diagnosis. Do not tape the knob down or bypass the safety switch — that defeats the exact protection that keeps your family safe.

No hot water and the pilot will not stay lit? Call (888)239-9523 to speak with a local plumbing professional about a same-day water heater diagnostic visit.

A Thermocouple That Has Failed

The thermocouple is the most common reason a pilot will not stay lit. It is a thin metal probe positioned in the pilot flame, and over years of heat cycling it degrades, corrodes, or shifts out of the flame. A thermocouple that is slightly misaligned can behave exactly like a failed one.

Signs that point to the thermocouple include a pilot that lights easily but dies within seconds of releasing the knob, a flame that looks healthy yet will not hold, or a heater that worked fine until the pilot suddenly started dropping out.

Replacing a thermocouple is a modest repair for someone comfortable working on gas appliances, but it involves the gas control valve, the burner compartment, and a precise fit. If the fitting is cross-threaded or the probe is not fully in the flame, the heater may run briefly and then shut down again. On many modern heaters the thermocouple is part of a sealed pilot assembly that is not designed for homeowner replacement.

Drafts, Dirty Orifices, and Blocked Vents

When the thermocouple tests fine, the next suspects are airflow and fuel delivery. A pilot flame needs a steady supply of gas and clean air, and either can be interrupted:

• Drafts: a nearby furnace, dryer, bathroom fan, or a door that slams can pull air across the pilot and blow it out. Sealing gaps and keeping closet doors positioned as the manufacturer specifies often solves repeat outages.
• Dirty pilot orifice: dust, lint, and spider webs clog the tiny opening. A flame that is yellow, weak, or only lights partway suggests a restricted orifice. Cleaning it requires disassembly and should be done carefully by someone familiar with gas burners.
• Blocked vent or flue: a bird nest, collapsed liner, or disconnected pipe causes poor draft and can extinguish the pilot. This is a safety issue, not a convenience issue.
• High wind or negative pressure: a water heater sharing space with a powerful exhaust fan can experience backdraft, especially in tightly sealed newer homes.

Carbon monoxide is the real risk with venting problems. If the pilot keeps going out after a vent or draft issue, do not keep relighting it and hoping for the best — have the venting inspected.

When to Call a Professional Plumber

Call a plumbing professional for any of these situations:

• The pilot will not stay lit after two careful relight attempts.
• You smell gas at any point, or the burner flame is yellow and lazy instead of blue.
• The vent pipe is loose, rusted, or blocked, or the area feels excessively hot.
• The thermocouple or pilot assembly needs replacement inside a sealed burner compartment.
• The heater is over ten years old and has repeated pilot or burner problems.
• You are uncomfortable working near a gas valve, or the instructions on the label do not match what you see.

A pilot that quits repeatedly is often the first sign of a component nearing the end of its life. Sometimes a thermocouple or pilot assembly restores reliable service; other times the tank itself is failing and replacement makes more sense than repeated repairs. A technician can test the flame sensor, check draft, and confirm the unit is venting safely.

Relighting a pilot is a five-minute job. Finding out why it keeps going out takes a methodical look at the thermocouple, the air supply, and the venting — and those checks matter for safety as much as for comfort. If the flame drops out again after a relight, stop repeating the process and have the system inspected. Explore our full range of plumbing services or call us at (888)239-9523 and we will connect you with a local plumbing professional who can diagnose the pilot and get your hot water back.