Water Heater Pilot Light Won't Stay Lit: Causes and Fixes

If your water heater's pilot light goes out the moment you let go of the control knob, the most likely culprit is the thermocouple — the small safety sensor that sits in the pilot flame and tells the gas valve it is safe to keep gas flowing. When that sensor is dirty, bent, worn out, or simply not getting hot enough, the valve shuts the gas off on purpose, and the pilot dies. The good news: the fix is often a cleaning, a repositioning, or a cheap part. The rest of this guide walks through how to relight the pilot safely, how to read what the flame is telling you, and how to work through the causes in order — plus the points where you should stop and call a plumber in Lawrenceville.

Safety First: Read This Before You Touch Anything

Gas water heaters are safe to live with and unforgiving to guess at, so two rules come before everything else.

• If you smell gas — a rotten-egg odor — do not try to relight anything, do not flip light switches or appliances, and do not stay in the room to investigate. Leave the house and call your gas utility or 911 from outside. A pilot problem is never worth a gas-exposure risk.
• Never work on the gas control valve, the gas supply line, or gas connections yourself. Those are licensed-plumber jobs. Everything in the homeowner-safe section below stays on the outside of that line: relighting, cleaning dust and soot from accessible parts, and checking for drafts.

Also stop and call a pro if you see soot buildup, melted or scorched parts, or heavy rust inside the burner chamber. Soot in particular can point to a venting or combustion problem that a relight will not fix.

How the Pilot Light Stays Lit (And Why It Goes Out by Design)

A standing-pilot gas water heater keeps a tiny flame burning all the time. That flame does two jobs: it stands ready to ignite the main burner whenever the thermostat calls for heat, and it heats the tip of the thermocouple.

The thermocouple is a thin copper rod — really two dissimilar metals joined at one end — with its tip sitting directly in the pilot flame. Heated by the flame, it generates a tiny electrical current, commonly cited at roughly 20 to 30 millivolts. That current powers a small magnet inside the gas control valve, holding the valve open so gas keeps flowing to the pilot.

That is the whole safety trick: if the pilot flame goes out, the thermocouple cools, the current stops, and the valve snaps shut, cutting off the gas before it can accumulate in your home. So when your pilot "won't stay lit," the heater is usually not being stubborn — its safety system is doing exactly what it was built to do, because something is stopping the thermocouple from proving the flame. The diagnostic job is figuring out which something.

One scope note: this guide is for standing-pilot tank water heaters. If your unit has electronic ignition, there is no constant pilot flame to relight, and the troubleshooting is different. Tankless gas units likewise use electronic ignition and flame sensors rather than a standing pilot — our gas vs. electric water heater guide explains which type you have if you are unsure.

How to Relight the Pilot Correctly

Many "failed" pilots are just a relight done too fast. Before you replace anything, try the procedure properly — it is also the test that points at the thermocouple.

1. Turn the gas control knob to OFF and wait at least 5 minutes. This lets any unburned gas around the burner clear. Do not skip the wait.
2. Turn the knob to PILOT. This restricts gas flow to the pilot burner only.
3. Press and hold the knob down, then light the pilot with the built-in igniter button or a long lighter, depending on your model. Keep holding the knob down while the flame burns.
4. Keep holding for 30 to 60 seconds — longer, up to 90 seconds, on some sealed-combustion models. This is the step people cut short: the thermocouple needs that time to heat up and start generating current.
5. Release the knob slowly. If the pilot stays lit, turn the knob to ON and check that the main burner ignites. If it goes out the instant you release, that is the classic thermocouple symptom — keep working through the causes below.

Follow the lighting instructions printed on your unit's label if they differ from these general steps; the label wins for your model. And if the pilot will not light at all after two careful attempts, stop trying — repeated attempts with gas flowing are how a small problem becomes a dangerous one.

Read the Flame: What a Healthy Pilot Looks Like

Before you take anything apart, look at the pilot flame through the sight glass while it is lit (hold the knob down if you have to).

• Healthy: steady, mostly blue, and wrapping the top half-inch or so of the thermocouple tip. A flame like this that still dies on release points squarely at the thermocouple itself.
• Weak, small, or lazy: the flame barely reaches the sensor, or flickers and lifts off it. This usually means the pilot is not getting enough gas or air — a clogged pilot orifice or tube, or a blocked air intake.
• Yellow or orange-tipped and dancing: this points to incomplete combustion or a dirty burner area — dust, lint, or soot interfering with the flame. A yellow flame also deserves a pro's eye if cleaning does not restore a clean blue burn, because it can signal a venting issue.
• Blowing sideways or sputtering out: a draft is deflecting the flame off the sensor. This is common in garages and basement utility areas in Lawrenceville homes, where a nearby exterior door, a dryer vent, or a furnace fan can create moving air right across the burner chamber.

The flame reading narrows the whole job: a good flame that dies means sensor; a bad flame means fuel or air delivery; a flame that will not sit still means drafts.

Cause 1: Drafts and Poor Air Supply

A pilot flame is small, and it does not take much air movement to push it off the thermocouple tip. Check for an open vent, a fan, or a door that creates a cross-breeze near the heater, and close off the draft if you can do so without blocking the unit's combustion air supply — the heater still needs fresh air to burn safely.

Also check the air intake and burner area for dust and lint. On flammable-vapor-ignition-resistant (FVIR) units, common on heaters made after 2003, the burner chamber is sealed behind a manifold door with a gasket. If that door has been opened, inspect the gasket: a damaged or poorly seated gasket affects combustion and can be a carbon monoxide risk, so replace it with the correct part before running the heater. A gentle cleaning of lint and dust from the intake screen and burner area — with the gas off — restores airflow on many units that "mysteriously" started losing their pilot after years of quiet service.

Cause 2: A Clogged Pilot Orifice or Tube

The pilot orifice is a tiny opening, and it clogs easily with dust, soot, or debris over time. A partially blocked orifice produces exactly the weak, yellow, or dancing flame described above — not enough heat reaching the thermocouple, so the valve closes.

Cleaning a pilot tube is sometimes done with a puff of compressed air or a thin wire, but take care not to enlarge the opening, and never poke around inside the gas valve itself. If you are not comfortable working around the burner assembly, or the flame does not improve after cleaning the accessible parts, this is a good place to hand the job to a plumber rather than escalate the disassembly yourself.

Cause 3: A Dirty, Bent, or Failing Thermocouple

This is the most common cause, and it is worth understanding the three ways a thermocouple fails.

• Dirty: soot or carbon buildup coats the tip and insulates it from the flame's heat. After shutting off the gas and letting things cool, the tip can sometimes be cleaned gently with fine-grit emery cloth or steel wool until the metal is bright again. Reinstall it so the tip sits squarely in the flame, then relight and test.
• Bent or misaligned: the tip has been knocked out of the flame's path — during other work, or by years of vibration — so the flame heats air instead of metal. Repositioning it so the flame fully envelops the tip solves this without any parts at all.
• Worn out: thermocouples simply age. A sensor that reads well below the healthy millivolt range, or that keeps failing after cleaning and repositioning, needs replacing. Universal thermocouples are inexpensive parts, typically in the $10–$30 range, and swapping one is a manageable job for a confident DIYer: shut off the gas, unscrew the mounting nut at the gas control valve and the bracket at the pilot assembly, install the new one the same way, and tighten the nut snugly — hand-tight first to avoid cross-threading, then about a quarter-turn with a wrench. After relighting, check the gas connection with soapy water; bubbles mean a leak, and that means shutting the gas off and calling a pro.

Note that some models use a thermopile instead of a single thermocouple — essentially several sensors in series producing a higher voltage. The symptoms are the same, but the part and the testing differ, so match the replacement to your model number rather than assuming a universal thermocouple fits.

Cause 4: A Tripped Thermal Cutoff Switch

Many gas heaters have a thermal cutoff or high-limit switch that trips if the burner area overheats, and a tripped switch can keep the pilot from staying lit. Some models allow a reset following the manufacturer's instructions; others require replacement once tripped. If you find a tripped switch, treat it as a symptom, not just a button to push — something caused the overheat, whether a blocked vent, a lint-clogged intake, or a failing control. Reset once if your manual clearly describes how; if it trips again, call a plumber to find the underlying cause.

Cause 5: Gas Supply Problems

Check the obvious before assuming a part has failed: is the gas supply valve to the heater fully open? Has your gas service been interrupted, or has other gas work just been done in the house? A partly closed valve or a supply interruption starves the pilot just as surely as a clogged orifice. If the supply looks fine and other gas appliances in the house are working, the problem is inside the heater, not upstream of it — and anything beyond the heater's shutoff valve belongs to the gas utility or a licensed plumber.

Cause 6: A Failing Gas Control Valve

If the pilot flame is strong and blue, the thermocouple is new and correctly positioned, the air supply is clean, and the pilot still will not stay lit, the gas control valve itself is the remaining suspect. The valve contains the electromagnet the thermocouple's current is supposed to hold open, and when that mechanism fails, no sensor swap will fix it. Gas valve replacement is a pro-only job and the expensive endpoint of this diagnosis — several hundred dollars in most published ranges — which is also the point where the age of the heater starts to matter. Our repair-or-replace guide walks through the math: on a heater past 10–12 years, a costly valve job is often the moment replacement wins.

What a Pilot Repair Typically Costs

Prices vary by model, part, and market, so treat these as typical ranges from plumbing guides rather than a quote. A universal thermocouple part runs roughly $10–$30; a professional thermocouple replacement, parts and labor together, is commonly cited around $100–$300. A thermopile or a gas control valve costs more, and valve replacement can run several hundred dollars before labor. If your heater is older and the repair estimate approaches half the cost of a new unit, get a replacement quote alongside the repair quote — that comparison is usually what settles the decision. Our water heater repair cost guide breaks down the same ranges by part and situation.

When to Call a Pro in Lawrenceville

Call a plumber rather than continuing to troubleshoot if any of these apply:

• You smell gas at any point, or a soapy-water check shows bubbles at a gas connection.
• The pilot stays out after a correct relight plus a thermocouple cleaning or replacement.
• The flame stays yellow after cleaning, or you see soot, scorching, or heavy rust in the burner chamber.
• The main burner will not ignite even though the pilot stays lit — that points to the gas valve or an internal sensor.
• The thermal cutoff keeps tripping, or the unit is a sealed-combustion model you are not sure how to open safely.
• The heater is leaking, or the tank itself is visibly corroded — that is a replacement conversation, not a pilot repair.

Water Heater Pros handles emergency water heater repair across Lawrenceville and Gwinnett County, so a pilot that has left you without hot water does not have to wait for a weekday appointment. A standard visit also covers the things a pilot check often uncovers — sediment, a tired anode rod, a weeping T&P valve — which our water heater maintenance guide puts into the full annual routine.

A pilot light that will not stay lit is annoying, but it is also informative: the heater is telling you, through its own safety system, exactly where the fault sits. Relight it correctly, read the flame, and work the causes in order — drafts and air, pilot orifice, thermocouple, thermal switch, gas supply, gas valve — and most of the time you will find the answer before you reach the end of the list. And when the answer turns out to be the gas valve, or anything that smells like gas, the right fix is a professional's visit, not a third attempt at the knob.