Pilot Light & Ignition Problems

Last updated September 24, 2026

A pilot that won't stay lit, or an igniter that clicks without lighting, is one of the most common gas water heater calls, and one of the clearest cases where altitude can be a genuine factor.

Common causes

A failed thermocouple or flame sensor, a dirty or misaligned pilot assembly, a weak igniter, or a closed or restricted gas supply are the usual causes. Occasionally, a draft near the unit repeatedly blows out the pilot flame.

Where altitude fits in

Combustion changes with elevation, and a unit that was never configured correctly for its address can show up as exactly this symptom, a pilot that's difficult to keep lit or that behaves inconsistently. That doesn't mean altitude is always the cause, but it's a genuine possibility worth raising, especially if the problem has been recurring rather than a one-time event.

What's safe to try, and what isn't

Relighting the pilot following the exact steps on the manufacturer's label is generally fine. Do not attempt to adjust the gas control valve, bypass a safety switch, or disassemble the pilot assembly. If you smell gas at any point, leave the house and call your gas utility and emergency services from outside.

How it gets fixed

The technician tests the thermocouple or flame sensor, checks the igniter, inspects the pilot assembly for buildup or misalignment, and confirms gas supply and, if relevant, that the unit's configuration matches its elevation.

What a technician checks in order

Gas supply and shutoff valve position, thermocouple or flame sensor condition, igniter function, and pilot assembly cleanliness are typically checked in that order, since it moves from the simplest to the more involved possible causes.

Documenting the pattern before you call

Noting how many times the pilot has gone out, roughly how long between failures, and whether it happens in any particular weather or usage pattern gives the technician more to work with than a single description.

When It's Bigger Than the Pilot

If pilot problems turn out to trace back to venting or altitude configuration rather than a single worn part, see our venting & combustion air and high-altitude sizing pages for the deeper explanation.

How a Standing Pilot Works

On a traditional gas water heater, a small pilot flame burns constantly and heats a thermocouple. The thermocouple generates a tiny voltage that holds the gas valve's safety magnet open. If the pilot goes out, the thermocouple cools, the voltage drops and the valve shuts off gas to both pilot and burner. That's a safety feature, and it's why a weak thermocouple causes a pilot that won't stay lit.

Common Causes of Pilot Outages

A weak or misaligned thermocouple, a dirty pilot orifice, a draft blowing out the flame, a tripped flammable-vapor sensor, or inadequate combustion air are the most common causes. In Colorado, altitude reduces burner margin and wind can downdraft through short flues, so pilot problems are more common than at sea level.

Flammable-Vapor Sensors

Modern gas water heaters have a flammable-vapor sensor and a flame arrestor at the combustion chamber. If the sensor detects vapors, or if lint and dust clog the arrestor, the unit shuts down and may lock out. Cleaning the arrestor screen and addressing the source of vapors or dust often resolves it; in some models, a tripped sensor requires replacement of the gas control.

Electronic Ignition Units

Many newer gas water heaters use electronic ignition with a hot-surface igniter or spark igniter and a flame sensor. Power-vent models add a blower and pressure switch. If one of these components fails, the unit won't light. Error codes or LED flash patterns on the control usually indicate the fault.

Relighting Safely

Relighting instructions are on the label on the tank. If you smell gas, don't relight; leave the house and call the utility. If the pilot won't stay lit after one or two attempts, stop and call for service rather than repeatedly relighting.

When to Replace the Gas Control

If the thermocouple and pilot are good but the unit still won't stay lit, the gas control valve may be faulty.

A Typical Colorado Case

In an Evergreen home at about 7,200 feet, a gas water heater's pilot goes out several times a week, especially on windy days. The technician finds a short roof vent without a proper cap and a thermocouple that's weakened with age. Installing a new thermocouple and a listed vent cap, and confirming the unit's high-altitude rating, stops the outages.

Questions Homeowners Ask

Why does my pilot go out when the dryer runs? The dryer may depressurize the room and pull air down the vent; combustion air needs addressing.

Is it safe to keep relighting? Not repeatedly; call for diagnosis.

Why won't my electronic ignition unit light? Check error codes; a failed igniter or flame sensor is common.

Thermocouples, Thermopiles and Flame Sensors

A thermocouple produces about 25 to 35 millivolts when heated by a healthy pilot, enough to hold a standard gas valve open. A thermopile is a cluster of thermocouples producing several hundred millivolts, used on controls that need more power, including many flammable-vapor-resistant models. Electronic-ignition units use a flame sensor, a metal rod that conducts a tiny current through the flame to prove ignition. Each can weaken, crack or get coated with soot. A technician tests output with a meter rather than guessing.

Wind, Downdrafts and Mountain Homes

In Colorado's foothills and mountains, wind can blow down a short roof vent and extinguish a pilot. Houses on ridges or in canyons with strong gusts see this most often. A listed vent cap, adequate vent height above the roof and proper combustion air usually stop it. Where they don't, a sealed-combustion or power-vent water heater eliminates the draft hood entirely.

Lint, Dust and Combustion Air

Laundry lint, pet hair and construction dust clog the flame arrestor screen on modern gas water heaters. The burner then starves for air, the flame lifts or goes yellow and the flammable-vapor sensor may trip. Cleaning the arrestor and keeping the area around the heater clean are simple preventive steps, especially where the water heater shares a room with the dryer.

When Pilot Problems Point to Bigger Issues

If a pilot goes out repeatedly despite a new thermocouple and clean burner, the cause may be a failing gas control, low gas pressure, a blocked vent or backdrafting from depressurization. Those conditions can also create carbon monoxide risk, which is why persistent pilot problems deserve a full diagnosis.

Wind, Drafts and Altitude

A pilot that goes out on windy days is a common Colorado complaint, particularly in canyon-mouth towns and on the plains. Strong gusts can push air back down a short or poorly capped flue and snuff the pilot, and at altitude a pilot flame has less margin to begin with. A proper vent cap, adequate flue height above the roof and a check of the draft hood usually solve it.

Indoor drafts matter too. A water heater near an exterior door, a clothes dryer or a powerful kitchen exhaust fan can be starved of combustion air when those are running, so the burner struggles or the thermocouple cools and shuts the gas off.