Pilot Light Keeps Going Out? A Detailed Guide to Gas Boiler Ignition Problems

When a boiler’s pilot light keeps going out, it’s rarely random. In most cases, it’s the boiler telling you that a safety component, ignition part, or airflow condition isn’t quite right.

Homeowners in the Denver area tend to notice this problem more during winter, when boilers cycle more frequently and even small ignition issues become impossible to ignore. While relighting the pilot may get heat back temporarily, repeated flame failure almost always points to an underlying issue that needs attention.

This guide explains how pilot systems actually work, the real-world reasons they fail, what’s safe to observe as a homeowner, and when continued relighting becomes unsafe.

A Quick Safety Reminder

Gas ignition issues should always be treated with caution.

If you smell gas, hear hissing near the boiler, or the pilot refuses to stay lit after a couple of attempts, stop troubleshooting and contact a professional. Never try to adjust gas valves, sensors, or safety controls.

How a Boiler Pilot System Works

On boilers with standing pilots, the pilot light is a small, continuously burning flame that serves two critical purposes:

1. Ignition – It lights the main burner when the thermostat calls for heat
2. Safety verification – It proves that gas is burning properly before allowing full gas flow

The pilot flame heats a safety sensor (usually a thermocouple). If that sensor detects heat, the gas valve stays open. If the flame goes out, gas flow shuts off automatically.

This design prevents unburned gas from accumulating — which is why a boiler will not run at all if the pilot can’t stay lit.

What “Pilot Light Keeps Going Out” Really Tells a Technician

From a technician’s perspective, repeated pilot failure usually means one of three things:

• The flame isn’t strong or stable enough
• The flame is present, but the safety sensor can’t “see” it properly
• Something external (airflow, pressure, or gas supply) is interfering

Each of these categories has common causes.

The Most Common Causes of Repeated Pilot Failure

1. Thermocouple Problems (Most Frequent Cause)

The thermocouple is a small metal probe positioned directly in the pilot flame. Its only job is to sense heat and tell the gas valve, “Yes, the flame is burning safely.”

Over time, thermocouples:

• Wear out from constant heating and cooling
• Become coated with soot or oxidation
• Shift slightly out of the flame path

When this happens, the sensor may cool too quickly or fail to generate the signal needed to keep the gas valve open.

Typical pattern homeowners notice:

• Pilot lights normally
• Flame looks okay at first
• Pilot goes out after 10–60 seconds

This is one of the most common ignition repairs technicians perform on older gas boilers.

2. Weak or Dirty Pilot Flame

A pilot flame needs to be strong, steady, and properly shaped to heat the thermocouple.

Dust, lint, rust flakes, or debris can partially block the pilot orifice, resulting in:

• A small flame
• A flame that flickers
• A flame that doesn’t fully contact the sensor

In basements, utility rooms, or older Denver homes, this buildup happens gradually and often goes unnoticed until ignition problems begin.

3. Drafts and Airflow Issues (Often Overlooked)

Pilot flames are sensitive. Even moderate airflow changes can blow them out.

Draft issues may come from:

• Loose or damaged venting
• Negative pressure caused by exhaust fans
• Doors or windows near the boiler
• Changes in airflow during winter when homes are sealed tightly

Technicians often see pilot issues that only happen:

• At night
• During very cold weather
• After home upgrades that affect airflow

4. Gas Supply or Pressure Irregularities

If gas pressure is inconsistent, the pilot flame may be unstable or extinguish unexpectedly.

This can be caused by:

• Issues with the gas valve
• Supply pressure fluctuations
• Problems affecting multiple gas appliances

If other gas appliances show symptoms, that’s an important clue — and a reason to stop DIY attempts.

5. Failing Gas Valve (Less Common, More Serious)

Gas valves contain internal safety mechanisms. When they begin to fail, they may:

• Shut off gas prematurely
• Fail to hold the pilot open
• Prevent reliable relighting

Gas valve problems always require professional testing and replacement.

What a Healthy Pilot Flame Should Look Like

While you shouldn’t adjust the flame yourself, observing it is safe.

A healthy pilot flame is typically:

• Mostly blue
• Steady, not flickering
• Large enough to fully envelop the thermocouple

A yellow, weak, or wavering flame usually indicates contamination, airflow problems, or gas issues.

Is It Safe to Keep Relighting the Pilot?

Occasional relighting can be acceptable only if:

• You follow the manufacturer’s instructions
• You do not smell gas
• The pilot has gone out once
• The flame stays lit afterward

However, repeated relighting is a warning sign, not a solution.

Each failed ignition attempt:

• Stresses safety components
• Masks the real issue
• Increases the chance of unexpected shutdowns

Why Ignoring Pilot Problems Can Lead to Bigger Issues

Continued pilot failure can result in:

• Loss of heat during cold weather
• Increased wear on ignition components
• Unreliable boiler operation
• Emergency breakdowns during winter

In Denver winters, an unreliable pilot can quickly turn into a no-heat situation.

When It’s Time to Call a Professional

You should schedule service if:

• The pilot will not stay lit
• You’ve relit it more than once
• The boiler shuts down shortly after firing
• The flame looks weak or unstable
• You suspect gas supply or venting issues

A professional technician can:

• Test and replace the thermocouple
• Clean the pilot assembly safely
• Check venting and draft conditions
• Verify gas valve operation and pressure

If ignition problems persist, it’s safest to arrange professional boiler repair in Denver.

Final Thoughts

A pilot light that keeps going out isn’t just an inconvenience — it’s a built-in safety system telling you something needs attention. While a one-time outage can happen, repeated failures usually mean a component or airflow issue is developing.

Addressing pilot problems early helps ensure consistent heat, safer operation, and fewer winter emergencies.