Why Your Gas Fireplace Pilot Light Won't Stay Lit (And How to Fix It)

If your gas fireplace lights for a moment and the pilot flame winks out the second you release the control knob, you are not alone — it is one of the most common service calls we run across Stone Oak, Alamo Heights, and the rest of San Antonio.

The good news: a pilot that will not stay lit is almost always a safety circuit doing its job. Your fireplace is designed to close the gas valve the moment it cannot confirm the pilot flame is lit. The culprit is usually a worn sensor, a clogged pilot orifice, or a gas supply problem — not a mystery.

1. A Dirty or Failing Thermopile (The #1 Cause)

The thermopile sits in the pilot flame and generates the small electrical current that holds the gas valve open. When it weakens, the valve clicks shut as soon as you release the knob.

Signs it is the thermopile:

• The pilot stays lit while the knob is depressed but dies immediately after release
• The main burner is slow to ignite, or the fireplace shuts down after 10-20 minutes of running
• The pilot flame looks small, yellow-tipped, or lazy instead of blue and crisp

A thermopile is an inexpensive part, but testing and replacing it means removing the log set and working around a live gas valve — a job for a factory-trained technician.

2. A Worn-Out Thermocouple

Older San Antonio fireplaces often use a thermocouple instead of a thermopile. It does the same job — proving the pilot is lit — but produces a weaker signal. A thermocouple that has grayed or shows a white-hot worn tip will drop out intermittently, especially on cold mornings when the fireplace has sat idle since last winter.

3. A Clogged Pilot Orifice

The pilot orifice is a pinhole-sized opening. Dust, pet hair, lint from household carpet, and even tiny spider webs (very common in Texas homes after a summer of disuse) can restrict it. A starved pilot produces a weak flame that cannot keep the thermocouple or thermopile hot enough, so the valve shuts.

4. Low Gas Pressure

If the pilot and main burner both struggle, the problem may be upstream: a half-open gas valve, a failing regulator, or an undersized gas line shared with other appliances. Low pressure is not a DIY diagnosis — it requires a manometer and a qualified technician.

When to Call a Factory-trained Technician Instead of Relighting

DIY relighting is fine for a healthy fireplace after a summer shutdown. Call a professional when:

• The pilot dies repeatedly within minutes of relighting
• You smell gas near the unit, even faintly
• The pilot flame is yellow, orange, or touching surrounding components
• The main burner pops, surges, or delays more than a few seconds
• The fireplace has not been professionally inspected in over 12 months

Our technicians carry thermocouples, thermopiles, and pilot assemblies on the truck, so most pilot problems are solved in a single same-day visit across San Antonio, Stone Oak, and Boerne.

The Bottom Line

A dying pilot light is your fireplace telling you it needs service. Fix the sensor or the blockage once, and it will stay lit through every cold snap South Texas throws at it. If yours will not stay lit, book our 20-point tune-up and we will diagnose it the same week.