Gas Pilot Will Not Stay Lit?

"The pilot will not stay lit." You hold the knob, the little flame catches, you count to thirty, you let go, and it dies. Or the pilot holds, the burner comes up, and twenty minutes later the whole fire drops out on its own. Some owners also notice a smell they cannot place, or a gray film creeping across the glass.

Before anything else, one rule.

If you smell gas, leave first

Gas companies add a sulfur odor, like rotten eggs, so leaks can be noticed. If that smell is in the room, do not try to relight anything, do not flip switches, and do not use a phone inside the house. Get everyone out, then call your gas utility's emergency line from outside. They come out to check for leaks, and that check should happen before any fireplace company touches the unit.

A different smell, sharp or oily or like hot dust, is a service question rather than an emergency. A carbon monoxide alarm going off is an emergency. Shut the fireplace off, open windows, get out, and call 911 if anyone feels dizzy, sick, or unusually tired.

With that covered, here is what is usually going on.

How the pilot knows to stay on

A gas fireplace will only let gas flow to the pilot while it can prove there is a flame. The proof comes from a small metal probe sitting in the pilot flame. Heat that probe and it produces a tiny electrical signal, a few thousandths of a volt. That signal holds a magnet in the gas valve open. Lose the flame, the probe cools, the signal fades, the magnet lets go, and gas stops. That probe is the thermocouple.

Many fireplaces add a second, larger probe called a thermopile. It works the same way but makes enough power to run the main burner valve and the wall switch or remote. If the thermopile weakens, the pilot may stay lit while the burner refuses to come on, or comes on and then drops out.

Both parts wear. Years of flame contact erode the tip, and a loose connection at the valve cuts the signal just as surely.

Five common causes

A worn or misaligned thermocouple

If the pilot dies the moment you release the knob, this is the first suspect. Sometimes the probe has only shifted out of the flame and needs repositioning. Often it is worn and needs replacing.

A dirty pilot assembly

Spiders love pilot tubes. Lint, dust, and rust flakes do too. A clogged pilot burns small, yellow, and lazy, and a weak flame does not heat the probe enough to hold the valve open. The pilot should be a firm blue flame wrapping the tip of the thermocouple. If yours looks thin or flickers away from it, cleaning may solve the whole problem.

A tired thermopile

The burner turns on slowly, cuts out after a while, or ignores the remote. A meter reading at the valve tells us whether the thermopile is producing what it should.

A faulty valve

Less common, but valves do fail. When the sensors test fine and the pilot is clean, the valve is next on the list. Replacement parts depend on the make and model.

A blocked or damaged vent

This one matters most. A direct-vent fireplace draws outside air in and pushes exhaust out through a two-layer pipe, one inside the other. If a bird nest, debris, or a crushed section blocks that pipe, exhaust has nowhere to go. Many units have a sensor that shuts the burner down when it detects spillage, which looks like a fire that keeps dying. Ignoring it means running a fire that cannot breathe. Soot on the glass is another sign the burn is starved or the logs are out of position.

Soot on the glass

A light white haze is normal over a season. Black soot is not. It means incomplete combustion, from logs placed wrong, a burner port clogged, air shutter misadjusted, or a vent problem. Black soot also means more carbon monoxide is being produced. Stop using the unit until it is checked, and keep a working carbon monoxide alarm in the room.

What a service visit covers

• - Testing the thermocouple and thermopile output with a meter.
• Cleaning the pilot assembly and burner ports.
• Checking pilot flame size and position.
• Inspecting log placement and the glass gasket.
• Checking the vent termination outside and the pipe for blockage, crushing, or separation.
• Leak testing the gas connections at the fireplace.
• Checking for carbon monoxide at the unit during a test burn.

Most of this falls under gas fireplace repair. If the unit has simply gone too long without service, gas fireplace cleaning handles the pilot, burner, glass, and logs in one visit.

What sets the bill

• - Which part has failed. A cleaned pilot costs far less than a new valve.
• The make, model, and age of the unit, since that decides whether parts are still made.
• Access to the valve, which sits behind a panel on some units and deep inside the firebox on others.
• Venting work, if the pipe or termination cap needs repair or replacement.
• Whether repair makes sense at all on a unit near the end of its life.

Repairs are priced in writing after we test the unit. When a unit is beyond repair, a gas insert in an existing wood fireplace typically costs $2,900 to $5,800, and a direct-vent gas fireplace runs $4,650 to $9,300. We would only bring that up after the testing says so.

If you want a sense of cost first, send the make and model from the rating plate, plus a photo of the pilot when lit, through the quote form.

When to call, and who to call

Call the gas utility first for any smell of gas, and leave the house to make that call. Call 911 for carbon monoxide symptoms. Call us for a pilot that keeps going out, a burner that shuts off, black soot on the glass, or an odd smell that is not gas. We service gas fireplaces across Pacific Palisades, Santa Monica, Brentwood, Beverly Hills and West Hollywood, and an older unit in a Pacific Palisades home is often a quick fix once the pilot is cleaned and the sensor is tested.

The phone link at the top of this page reaches us directly. Have the make and model handy if you can find it, and tell us what the pilot does just before it goes out.