Why does my water heater pilot keep going out and getting worse?

What's actually happening

Your water heater has a small standing pilot flame that's supposed to stay lit around the clock. A sensor called a thermocouple sits right in that flame and produces a tiny electrical signal, measured in millivolts.

That signal is the only thing telling the gas valve, 'yes, there's a flame here, keep the gas flowing.' When the signal drops, the valve slams shut. No gas, no pilot, no hot water.

So when your pilot keeps going out, the system isn't broken. It's refusing to let gas flow because it can't confirm a flame. That's the safety design working exactly as intended.

The word 'worsening' is the tell. A pilot that dies more and more often is describing a part that's slowly losing its grip. That's the classic signature of a thermocouple on its way out.

Why it's getting worse, not just failing

One-time pilot outages happen. A draft, a bump, a fluke. What matters here is the trend.

A dying thermocouple degrades gradually. First you notice you have to hold the knob a few seconds longer. Then it dies overnight. Then it won't make it through the afternoon. That escalating curve points straight at the sensor.

A dirty pilot orifice makes it worse in a different way. As grime narrows the opening, the flame shrinks and turns yellow, and a weak flame can't heat the thermocouple enough. So even a decent thermocouple starts failing to hold.

Sometimes both are happening at once, which is why I clean the orifice and test millivolts on the same visit. Fixing one and ignoring the other means you're back in a month.

Draft problems tend to be intermittent rather than steadily worsening. If your outages cluster on windy days or when the dryer that's a flue and air-supply issue, not a worn part.

What to do right now

Start with your nose. Get down near the base of the heater and smell for gas. A strong rotten-egg smell means stop, turn the control to OFF, get everyone out, and call the gas utility from outside.

No gas smell? Good. Turn the gas control knob to OFF and wait five full minutes. This clears any lingering gas before you try to relight. Don't rush it.

Now find the relight instructions. They're printed on a label on the tank or behind the burner access cover. Follow the exact sequence, because knob positions vary by model.

When you hit the pilot step, press and hold the knob down for the full time listed. You're heating the thermocouple tip so it can take over holding the valve open.

Release slowly. If the pilot dies the second you let go, the thermocouple isn't generating enough signal. Try once more. If it fails again, you've confirmed the part.

The single most useful thing you can do is time the failure. Dies instantly means thermocouple or bad connection. Dies after a few hours means a marginal flame or a slow valve. Dies on windy nights means draft.

• Dies immediately on knob release: thermocouple or loose connection
• Holds a minute then dies: weak pilot flame or dirty orifice
• Dies after hours, randomly: marginal thermocouple or failing valve
• Dies on windy days or with fans running: flue downdraft

What this costs in 2026

The parts here are cheap. That's the frustrating part. A thermocouple runs $12 to $25 at any hardware store. A thermopile for electronic-ignition units runs $30 to $60.

The labor is where the money goes. A pro thermocouple replacement typically lands between $200 and $800, including the diagnostic and the trip. That covers testing millivolts, cleaning the pilot assembly, and confirming a clean relight.

If it turns out to be the gas control valve, you're looking at $250 to $450 installed, sometimes more on sealed-combustion or FVIR units. At that price on an older tank, replacement enters the conversation.

A brand-new tank water heater installed runs roughly $1,600 to $2,600 in 2026, depending on size, gas versus electric, and how much venting or code upgrade your setup needs.

Just be honest with yourself about working on a gas appliance.

DIY or call a pro

This one lands on the pro side of the line for most homeowners, and here's my honest reasoning.

The thermocouple swap is genuinely simple mechanically. You shut off the gas, disconnect three fittings, and reverse it. Plenty of handy people do it.

But it's inside a burner chamber on a gas appliance. If you don't reseat the burner correctly, or you overtighten the gas fitting, or you skip a leak check, the downside is a gas leak or a fire. That's a steep price for saving $150.

If you've worked with gas before, own a soap-solution leak test, and can read the millivolt spec, go for it. If any of that made you pause, call someone.

Anything involving the gas control valve, the flue, or an FVIR thermal switch is a licensed-pro job. No middle ground there.

• Reasonable DIY: cleaning lint from the base, checking for drafts, timing the failure, snugging a loose thermocouple nut
• Pro territory: replacing the thermocouple if you're unsure, gas valve work, flue and draft issues, FVIR resets

Can this wait?

Short answer: not long. This page is flagged as an emergency for good reasons.

The immediate risk is that you have no hot water, and if it's cold out, that goes from annoying to serious quickly (frozen mornings, no hot showers, and in extreme cold, other plumbing stress).

The bigger safety concern is fighting a failed relight. Every failed attempt where the pilot lights and dies puts a little unburned gas into the chamber. Do that over and over out of frustration and you're creating a hazard.

If the cause is backdrafting, waiting means potentially spilling carbon monoxide into your home whenever the pilot does burn. That's the version of this problem that actually hurts people.

My rule: try two clean relights following the label. If it won't hold, leave the gas OFF and get a pro out. Don't keep cycling it.

How your home's age changes this

Water heaters built after 2005 almost all have FVIR technology (flammable vapor ignition resistant). They pull combustion air through a screen at the base and have a one-shot thermal switch.

On these units, lint and dust around the base are a real cause of pilot trouble. The screen clogs, the unit starves for air, and it shuts down. Vacuuming that area is genuinely part of maintenance.

If your home is newer and built tight, backdrafting is more likely. Tight construction plus a powerful range hood or dryer can depressurize a utility closet enough to pull the flue backward.

Older homes (pre-2005) usually have simpler open-combustion heaters. Easier to service, but no vapor protection, so keep flammables away regardless.

If your tank predates 2015 and is acting up, check the manufacture date on the rating plate. Anything past 12 years is living on borrowed time, and I'd think hard before investing in repairs.

Why this often shows up in winter

A thermocouple that's marginal all summer can limp along fine. The first real cold snap often pushes it over the edge.

Heating season also runs your exhaust equipment harder. More dryer loads, more bath fan time, tighter closed-up house. All of that raises the odds of a downdraft snuffing the pilot.

Wind matters too. A stiff winter wind across the roof can reverse the flue draft on a poorly capped vent. If your outages started when the weather turned, mention that to whoever diagnoses it.

Bottom line: don't assume a winter-only pattern means the part is fine. Cold just reveals weaknesses that were already there.

How a tech actually diagnoses this

Here's the order a good tech works, so you know what you're paying for.

First, they observe the pilot flame and confirm it's blue, steady, and wrapping the thermocouple tip. A yellow or lazy flame changes the whole diagnosis.

Next, they test the thermocouple's open-circuit millivolts, then again under load. A healthy thermocouple reads roughly 25 to 30 mV open and should hold above about 20 mV when the valve's magnet is pulling. Weak readings confirm the part.

If the thermocouple checks out, they test the gas valve's magnet hold. A good signal that still won't keep the valve open points at the valve itself.

They also check draft at the flue and look for spillage, especially if you mentioned wind or fan-related outages. On FVIR units, they inspect the intake screen and the thermal switch.

Only after that do they replace a part. Anyone who swaps a thermocouple without testing first is guessing, and guessing is how you pay twice.